This patchset consolidates several changes in the capacity and the usage
tracking of the CPU. It provides a frequency invariant metric of the usage of
CPUs and generally improves the accuracy of load/usage tracking in the
scheduler. The frequency invariant metric is the foundation required for the
consolidation of cpufreq and implementation of a fully invariant load tracking.
These are currently WIP and require several changes to the load balancer
(including how it will use and interprets load and capacity metrics) and
extensive validation. The frequency invariance is done with
arch_scale_freq_capacity and this patchset doesn't provide the backends of
the function which are architecture dependent.
As discussed at LPC14, Morten and I have consolidated our changes into a single
patchset to make it easier to review and merge.
During load balance, the scheduler evaluates the number of tasks that a group
of CPUs can handle. The current method assumes that tasks have a fix load of
SCHED_LOAD_SCALE and CPUs have a default capacity of SCHED_CAPACITY_SCALE.
This assumption generates wrong decision by creating ghost cores or by
removing real ones when the original capacity of CPUs is different from the
default SCHED_CAPACITY_SCALE. With this patch set, we don't try anymore to
evaluate the number of available cores based on the group_capacity but instead
we evaluate the usage of a group and compare it with its capacity.
This patchset mainly replaces the old capacity_factor method by a new one and
keeps the general policy almost unchanged. These new metrics will be also used
in later patches.
The CPU usage is based on a running time tracking version of the current
implementation of the load average tracking. I also have a version that is
based on the new implementation proposal [1] but I haven't provide the patches
and results as [1] is still under review. I can provide change above [1] to
change how CPU usage is computed and to adapt to new mecanism.
Change since V9
- add a dedicated patch for removing unused capacity_orig
- update some comments and fix typo
- change the condition for actively migrating task on CPU with higher capacity
Change since V8
- reorder patches
Change since V7
- add freq invariance for usage tracking
- add freq invariance for scale_rt
- update comments and commits' message
- fix init of utilization_avg_contrib
- fix prefer_sibling
Change since V6
- add group usage tracking
- fix some commits' messages
- minor fix like comments and argument order
Change since V5
- remove patches that have been merged since v5 : patches 01, 02, 03, 04, 05, 07
- update commit log and add more details on the purpose of the patches
- fix/remove useless code with the rebase on patchset [2]
- remove capacity_orig in sched_group_capacity as it is not used
- move code in the right patch
- add some helper function to factorize code
Change since V4
- rebase to manage conflicts with changes in selection of busiest group
Change since V3:
- add usage_avg_contrib statistic which sums the running time of tasks on a rq
- use usage_avg_contrib instead of runnable_avg_sum for cpu_utilization
- fix replacement power by capacity
- update some comments
Change since V2:
- rebase on top of capacity renaming
- fix wake_affine statistic update
- rework nohz_kick_needed
- optimize the active migration of a task from CPU with reduced capacity
- rename group_activity by group_utilization and remove unused total_utilization
- repair SD_PREFER_SIBLING and use it for SMT level
- reorder patchset to gather patches with same topics
Change since V1:
- add 3 fixes
- correct some commit messages
- replace capacity computation by activity
- take into account current cpu capacity
[1] https://lkml.org/lkml/2014/10/10/131
[2] https://lkml.org/lkml/2014/7/25/589
Morten Rasmussen (2):
sched: Track group sched_entity usage contributions
sched: Make sched entity usage tracking scale-invariant
Vincent Guittot (9):
sched: add utilization_avg_contrib
sched: remove frequency scaling from cpu_capacity
sched: make scale_rt invariant with frequency
sched: add per rq cpu_capacity_orig
sched: get CPU's usage statistic
sched: replace capacity_factor by usage
sched; remove unused capacity_orig from
sched: add SD_PREFER_SIBLING for SMT level
sched: move cfs task on a CPU with higher capacity
include/linux/sched.h | 21 ++-
kernel/sched/core.c | 15 +--
kernel/sched/debug.c | 12 +-
kernel/sched/fair.c | 366 +++++++++++++++++++++++++++++++-------------------
kernel/sched/sched.h | 15 ++-
5 files changed, 271 insertions(+), 158 deletions(-)
--
1.9.1
Add new statistics which reflect the average time a task is running on the CPU
and the sum of these running time of the tasks on a runqueue. The latter is
named utilization_load_avg.
This patch is based on the usage metric that was proposed in the 1st
versions of the per-entity load tracking patchset by Paul Turner
<[email protected]> but that has be removed afterwards. This version differs from
the original one in the sense that it's not linked to task_group.
The rq's utilization_load_avg will be used to check if a rq is overloaded or
not instead of trying to compute how many tasks a group of CPUs can handle.
Rename runnable_avg_period into avg_period as it is now used with both
runnable_avg_sum and running_avg_sum
Add some descriptions of the variables to explain their differences
cc: Paul Turner <[email protected]>
cc: Ben Segall <[email protected]>
Signed-off-by: Vincent Guittot <[email protected]>
Acked-by: Morten Rasmussen <[email protected]>
---
include/linux/sched.h | 21 ++++++++++++---
kernel/sched/debug.c | 10 ++++---
kernel/sched/fair.c | 74 ++++++++++++++++++++++++++++++++++++++++-----------
kernel/sched/sched.h | 8 +++++-
4 files changed, 89 insertions(+), 24 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index cb5cdc7..adc6278 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1115,15 +1115,28 @@ struct load_weight {
};
struct sched_avg {
+ u64 last_runnable_update;
+ s64 decay_count;
+ /*
+ * utilization_avg_contrib describes the amount of time that a
+ * sched_entity is running on a CPU. It is based on running_avg_sum
+ * and is scaled in the range [0..SCHED_LOAD_SCALE].
+ * load_avg_contrib described the amount of time that a sched_entity
+ * is runnable on a rq. It is based on both runnable_avg_sum and the
+ * weight of the task.
+ */
+ unsigned long load_avg_contrib, utilization_avg_contrib;
/*
* These sums represent an infinite geometric series and so are bound
* above by 1024/(1-y). Thus we only need a u32 to store them for all
* choices of y < 1-2^(-32)*1024.
+ * running_avg_sum reflects the time that the sched_entity is
+ * effectively running on the CPU.
+ * runnable_avg_sum represents the amount of time a sched_entity is on
+ * a runqueue which includes the running time that is monitored by
+ * running_avg_sum.
*/
- u32 runnable_avg_sum, runnable_avg_period;
- u64 last_runnable_update;
- s64 decay_count;
- unsigned long load_avg_contrib;
+ u32 runnable_avg_sum, avg_period, running_avg_sum;
};
#ifdef CONFIG_SCHEDSTATS
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 8baaf85..578ff83 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -71,7 +71,7 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group
if (!se) {
struct sched_avg *avg = &cpu_rq(cpu)->avg;
P(avg->runnable_avg_sum);
- P(avg->runnable_avg_period);
+ P(avg->avg_period);
return;
}
@@ -94,7 +94,7 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group
P(se->load.weight);
#ifdef CONFIG_SMP
P(se->avg.runnable_avg_sum);
- P(se->avg.runnable_avg_period);
+ P(se->avg.avg_period);
P(se->avg.load_avg_contrib);
P(se->avg.decay_count);
#endif
@@ -214,6 +214,8 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
cfs_rq->runnable_load_avg);
SEQ_printf(m, " .%-30s: %ld\n", "blocked_load_avg",
cfs_rq->blocked_load_avg);
+ SEQ_printf(m, " .%-30s: %ld\n", "utilization_load_avg",
+ cfs_rq->utilization_load_avg);
#ifdef CONFIG_FAIR_GROUP_SCHED
SEQ_printf(m, " .%-30s: %ld\n", "tg_load_contrib",
cfs_rq->tg_load_contrib);
@@ -636,8 +638,10 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
P(se.load.weight);
#ifdef CONFIG_SMP
P(se.avg.runnable_avg_sum);
- P(se.avg.runnable_avg_period);
+ P(se.avg.running_avg_sum);
+ P(se.avg.avg_period);
P(se.avg.load_avg_contrib);
+ P(se.avg.utilization_avg_contrib);
P(se.avg.decay_count);
#endif
P(policy);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ee595ef..414408dd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -670,6 +670,7 @@ static int select_idle_sibling(struct task_struct *p, int cpu);
static unsigned long task_h_load(struct task_struct *p);
static inline void __update_task_entity_contrib(struct sched_entity *se);
+static inline void __update_task_entity_utilization(struct sched_entity *se);
/* Give new task start runnable values to heavy its load in infant time */
void init_task_runnable_average(struct task_struct *p)
@@ -677,9 +678,10 @@ void init_task_runnable_average(struct task_struct *p)
u32 slice;
slice = sched_slice(task_cfs_rq(p), &p->se) >> 10;
- p->se.avg.runnable_avg_sum = slice;
- p->se.avg.runnable_avg_period = slice;
+ p->se.avg.runnable_avg_sum = p->se.avg.running_avg_sum = slice;
+ p->se.avg.avg_period = slice;
__update_task_entity_contrib(&p->se);
+ __update_task_entity_utilization(&p->se);
}
#else
void init_task_runnable_average(struct task_struct *p)
@@ -1684,7 +1686,7 @@ static u64 numa_get_avg_runtime(struct task_struct *p, u64 *period)
*period = now - p->last_task_numa_placement;
} else {
delta = p->se.avg.runnable_avg_sum;
- *period = p->se.avg.runnable_avg_period;
+ *period = p->se.avg.avg_period;
}
p->last_sum_exec_runtime = runtime;
@@ -2512,7 +2514,8 @@ static u32 __compute_runnable_contrib(u64 n)
*/
static __always_inline int __update_entity_runnable_avg(u64 now,
struct sched_avg *sa,
- int runnable)
+ int runnable,
+ int running)
{
u64 delta, periods;
u32 runnable_contrib;
@@ -2538,7 +2541,7 @@ static __always_inline int __update_entity_runnable_avg(u64 now,
sa->last_runnable_update = now;
/* delta_w is the amount already accumulated against our next period */
- delta_w = sa->runnable_avg_period % 1024;
+ delta_w = sa->avg_period % 1024;
if (delta + delta_w >= 1024) {
/* period roll-over */
decayed = 1;
@@ -2551,7 +2554,9 @@ static __always_inline int __update_entity_runnable_avg(u64 now,
delta_w = 1024 - delta_w;
if (runnable)
sa->runnable_avg_sum += delta_w;
- sa->runnable_avg_period += delta_w;
+ if (running)
+ sa->running_avg_sum += delta_w;
+ sa->avg_period += delta_w;
delta -= delta_w;
@@ -2561,20 +2566,26 @@ static __always_inline int __update_entity_runnable_avg(u64 now,
sa->runnable_avg_sum = decay_load(sa->runnable_avg_sum,
periods + 1);
- sa->runnable_avg_period = decay_load(sa->runnable_avg_period,
+ sa->running_avg_sum = decay_load(sa->running_avg_sum,
+ periods + 1);
+ sa->avg_period = decay_load(sa->avg_period,
periods + 1);
/* Efficiently calculate \sum (1..n_period) 1024*y^i */
runnable_contrib = __compute_runnable_contrib(periods);
if (runnable)
sa->runnable_avg_sum += runnable_contrib;
- sa->runnable_avg_period += runnable_contrib;
+ if (running)
+ sa->running_avg_sum += runnable_contrib;
+ sa->avg_period += runnable_contrib;
}
/* Remainder of delta accrued against u_0` */
if (runnable)
sa->runnable_avg_sum += delta;
- sa->runnable_avg_period += delta;
+ if (running)
+ sa->running_avg_sum += delta;
+ sa->avg_period += delta;
return decayed;
}
@@ -2591,6 +2602,8 @@ static inline u64 __synchronize_entity_decay(struct sched_entity *se)
return 0;
se->avg.load_avg_contrib = decay_load(se->avg.load_avg_contrib, decays);
+ se->avg.utilization_avg_contrib =
+ decay_load(se->avg.utilization_avg_contrib, decays);
return decays;
}
@@ -2626,7 +2639,7 @@ static inline void __update_tg_runnable_avg(struct sched_avg *sa,
/* The fraction of a cpu used by this cfs_rq */
contrib = div_u64((u64)sa->runnable_avg_sum << NICE_0_SHIFT,
- sa->runnable_avg_period + 1);
+ sa->avg_period + 1);
contrib -= cfs_rq->tg_runnable_contrib;
if (abs(contrib) > cfs_rq->tg_runnable_contrib / 64) {
@@ -2679,7 +2692,8 @@ static inline void __update_group_entity_contrib(struct sched_entity *se)
static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
{
- __update_entity_runnable_avg(rq_clock_task(rq), &rq->avg, runnable);
+ __update_entity_runnable_avg(rq_clock_task(rq), &rq->avg, runnable,
+ runnable);
__update_tg_runnable_avg(&rq->avg, &rq->cfs);
}
#else /* CONFIG_FAIR_GROUP_SCHED */
@@ -2697,7 +2711,7 @@ static inline void __update_task_entity_contrib(struct sched_entity *se)
/* avoid overflowing a 32-bit type w/ SCHED_LOAD_SCALE */
contrib = se->avg.runnable_avg_sum * scale_load_down(se->load.weight);
- contrib /= (se->avg.runnable_avg_period + 1);
+ contrib /= (se->avg.avg_period + 1);
se->avg.load_avg_contrib = scale_load(contrib);
}
@@ -2716,6 +2730,27 @@ static long __update_entity_load_avg_contrib(struct sched_entity *se)
return se->avg.load_avg_contrib - old_contrib;
}
+
+static inline void __update_task_entity_utilization(struct sched_entity *se)
+{
+ u32 contrib;
+
+ /* avoid overflowing a 32-bit type w/ SCHED_LOAD_SCALE */
+ contrib = se->avg.running_avg_sum * scale_load_down(SCHED_LOAD_SCALE);
+ contrib /= (se->avg.avg_period + 1);
+ se->avg.utilization_avg_contrib = scale_load(contrib);
+}
+
+static long __update_entity_utilization_avg_contrib(struct sched_entity *se)
+{
+ long old_contrib = se->avg.utilization_avg_contrib;
+
+ if (entity_is_task(se))
+ __update_task_entity_utilization(se);
+
+ return se->avg.utilization_avg_contrib - old_contrib;
+}
+
static inline void subtract_blocked_load_contrib(struct cfs_rq *cfs_rq,
long load_contrib)
{
@@ -2732,7 +2767,7 @@ static inline void update_entity_load_avg(struct sched_entity *se,
int update_cfs_rq)
{
struct cfs_rq *cfs_rq = cfs_rq_of(se);
- long contrib_delta;
+ long contrib_delta, utilization_delta;
u64 now;
/*
@@ -2744,18 +2779,22 @@ static inline void update_entity_load_avg(struct sched_entity *se,
else
now = cfs_rq_clock_task(group_cfs_rq(se));
- if (!__update_entity_runnable_avg(now, &se->avg, se->on_rq))
+ if (!__update_entity_runnable_avg(now, &se->avg, se->on_rq,
+ cfs_rq->curr == se))
return;
contrib_delta = __update_entity_load_avg_contrib(se);
+ utilization_delta = __update_entity_utilization_avg_contrib(se);
if (!update_cfs_rq)
return;
- if (se->on_rq)
+ if (se->on_rq) {
cfs_rq->runnable_load_avg += contrib_delta;
- else
+ cfs_rq->utilization_load_avg += utilization_delta;
+ } else {
subtract_blocked_load_contrib(cfs_rq, -contrib_delta);
+ }
}
/*
@@ -2830,6 +2869,7 @@ static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
}
cfs_rq->runnable_load_avg += se->avg.load_avg_contrib;
+ cfs_rq->utilization_load_avg += se->avg.utilization_avg_contrib;
/* we force update consideration on load-balancer moves */
update_cfs_rq_blocked_load(cfs_rq, !wakeup);
}
@@ -2848,6 +2888,7 @@ static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq,
update_cfs_rq_blocked_load(cfs_rq, !sleep);
cfs_rq->runnable_load_avg -= se->avg.load_avg_contrib;
+ cfs_rq->utilization_load_avg -= se->avg.utilization_avg_contrib;
if (sleep) {
cfs_rq->blocked_load_avg += se->avg.load_avg_contrib;
se->avg.decay_count = atomic64_read(&cfs_rq->decay_counter);
@@ -3185,6 +3226,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
*/
update_stats_wait_end(cfs_rq, se);
__dequeue_entity(cfs_rq, se);
+ update_entity_load_avg(se, 1);
}
update_stats_curr_start(cfs_rq, se);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index dc0f435..65fa7b5 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -362,8 +362,14 @@ struct cfs_rq {
* Under CFS, load is tracked on a per-entity basis and aggregated up.
* This allows for the description of both thread and group usage (in
* the FAIR_GROUP_SCHED case).
+ * runnable_load_avg is the sum of the load_avg_contrib of the
+ * sched_entities on the rq.
+ * blocked_load_avg is similar to runnable_load_avg except that its
+ * the blocked sched_entities on the rq.
+ * utilization_load_avg is the sum of the average running time of the
+ * sched_entities on the rq.
*/
- unsigned long runnable_load_avg, blocked_load_avg;
+ unsigned long runnable_load_avg, blocked_load_avg, utilization_load_avg;
atomic64_t decay_counter;
u64 last_decay;
atomic_long_t removed_load;
--
1.9.1
From: Morten Rasmussen <[email protected]>
Adds usage contribution tracking for group entities. Unlike
se->avg.load_avg_contrib, se->avg.utilization_avg_contrib for group
entities is the sum of se->avg.utilization_avg_contrib for all entities on the
group runqueue. It is _not_ influenced in any way by the task group
h_load. Hence it is representing the actual cpu usage of the group, not
its intended load contribution which may differ significantly from the
utilization on lightly utilized systems.
cc: Paul Turner <[email protected]>
cc: Ben Segall <[email protected]>
Signed-off-by: Morten Rasmussen <[email protected]>
Signed-off-by: Vincent Guittot <[email protected]>
---
kernel/sched/debug.c | 2 ++
kernel/sched/fair.c | 3 +++
2 files changed, 5 insertions(+)
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 578ff83..a245c1f 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -94,8 +94,10 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group
P(se->load.weight);
#ifdef CONFIG_SMP
P(se->avg.runnable_avg_sum);
+ P(se->avg.running_avg_sum);
P(se->avg.avg_period);
P(se->avg.load_avg_contrib);
+ P(se->avg.utilization_avg_contrib);
P(se->avg.decay_count);
#endif
#undef PN
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 414408dd..d94a865 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2747,6 +2747,9 @@ static long __update_entity_utilization_avg_contrib(struct sched_entity *se)
if (entity_is_task(se))
__update_task_entity_utilization(se);
+ else
+ se->avg.utilization_avg_contrib =
+ group_cfs_rq(se)->utilization_load_avg;
return se->avg.utilization_avg_contrib - old_contrib;
}
--
1.9.1
Now that arch_scale_cpu_capacity has been introduced to scale the original
capacity, the arch_scale_freq_capacity is no longer used (it was
previously used by ARM arch). Remove arch_scale_freq_capacity from the
computation of cpu_capacity. The frequency invariance will be handled in the
load tracking and not in the CPU capacity. arch_scale_freq_capacity will be
revisited for scaling load with the current frequency of the CPUs in a later
patch.
Signed-off-by: Vincent Guittot <[email protected]>
Acked-by: Morten Rasmussen <[email protected]>
---
kernel/sched/fair.c | 7 -------
1 file changed, 7 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d94a865..e54231f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6042,13 +6042,6 @@ static void update_cpu_capacity(struct sched_domain *sd, int cpu)
sdg->sgc->capacity_orig = capacity;
- if (sched_feat(ARCH_CAPACITY))
- capacity *= arch_scale_freq_capacity(sd, cpu);
- else
- capacity *= default_scale_capacity(sd, cpu);
-
- capacity >>= SCHED_CAPACITY_SHIFT;
-
capacity *= scale_rt_capacity(cpu);
capacity >>= SCHED_CAPACITY_SHIFT;
--
1.9.1
From: Morten Rasmussen <[email protected]>
Apply frequency scale-invariance correction factor to usage tracking.
Each segment of the running_load_avg geometric series is now scaled by the
current frequency so the utilization_avg_contrib of each entity will be
invariant with frequency scaling. As a result, utilization_load_avg which is
the sum of utilization_avg_contrib, becomes invariant too. So the usage level
that is returned by get_cpu_usage, stays relative to the max frequency as the
cpu_capacity which is is compared against.
Then, we want the keep the load tracking values in a 32bits type, which implies
that the max value of {runnable|running}_avg_sum must be lower than
2^32/88761=48388 (88761 is the max weigth of a task). As LOAD_AVG_MAX = 47742,
arch_scale_freq_capacity must return a value less than
(48388/47742) << SCHED_CAPACITY_SHIFT = 1037 (SCHED_SCALE_CAPACITY = 1024).
So we define the range to [0..SCHED_SCALE_CAPACITY] in order to avoid overflow.
cc: Paul Turner <[email protected]>
cc: Ben Segall <[email protected]>
Signed-off-by: Morten Rasmussen <[email protected]>
Signed-off-by: Vincent Guittot <[email protected]>
---
kernel/sched/fair.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e54231f..7f031e4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2484,6 +2484,8 @@ static u32 __compute_runnable_contrib(u64 n)
return contrib + runnable_avg_yN_sum[n];
}
+unsigned long __weak arch_scale_freq_capacity(struct sched_domain *sd, int cpu);
+
/*
* We can represent the historical contribution to runnable average as the
* coefficients of a geometric series. To do this we sub-divide our runnable
@@ -2512,7 +2514,7 @@ static u32 __compute_runnable_contrib(u64 n)
* load_avg = u_0` + y*(u_0 + u_1*y + u_2*y^2 + ... )
* = u_0 + u_1*y + u_2*y^2 + ... [re-labeling u_i --> u_{i+1}]
*/
-static __always_inline int __update_entity_runnable_avg(u64 now,
+static __always_inline int __update_entity_runnable_avg(u64 now, int cpu,
struct sched_avg *sa,
int runnable,
int running)
@@ -2520,6 +2522,7 @@ static __always_inline int __update_entity_runnable_avg(u64 now,
u64 delta, periods;
u32 runnable_contrib;
int delta_w, decayed = 0;
+ unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu);
delta = now - sa->last_runnable_update;
/*
@@ -2555,7 +2558,8 @@ static __always_inline int __update_entity_runnable_avg(u64 now,
if (runnable)
sa->runnable_avg_sum += delta_w;
if (running)
- sa->running_avg_sum += delta_w;
+ sa->running_avg_sum += delta_w * scale_freq
+ >> SCHED_CAPACITY_SHIFT;
sa->avg_period += delta_w;
delta -= delta_w;
@@ -2576,7 +2580,8 @@ static __always_inline int __update_entity_runnable_avg(u64 now,
if (runnable)
sa->runnable_avg_sum += runnable_contrib;
if (running)
- sa->running_avg_sum += runnable_contrib;
+ sa->running_avg_sum += runnable_contrib * scale_freq
+ >> SCHED_CAPACITY_SHIFT;
sa->avg_period += runnable_contrib;
}
@@ -2584,7 +2589,8 @@ static __always_inline int __update_entity_runnable_avg(u64 now,
if (runnable)
sa->runnable_avg_sum += delta;
if (running)
- sa->running_avg_sum += delta;
+ sa->running_avg_sum += delta * scale_freq
+ >> SCHED_CAPACITY_SHIFT;
sa->avg_period += delta;
return decayed;
@@ -2692,8 +2698,8 @@ static inline void __update_group_entity_contrib(struct sched_entity *se)
static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
{
- __update_entity_runnable_avg(rq_clock_task(rq), &rq->avg, runnable,
- runnable);
+ __update_entity_runnable_avg(rq_clock_task(rq), cpu_of(rq), &rq->avg,
+ runnable, runnable);
__update_tg_runnable_avg(&rq->avg, &rq->cfs);
}
#else /* CONFIG_FAIR_GROUP_SCHED */
@@ -2771,6 +2777,7 @@ static inline void update_entity_load_avg(struct sched_entity *se,
{
struct cfs_rq *cfs_rq = cfs_rq_of(se);
long contrib_delta, utilization_delta;
+ int cpu = cpu_of(rq_of(cfs_rq));
u64 now;
/*
@@ -2782,7 +2789,7 @@ static inline void update_entity_load_avg(struct sched_entity *se,
else
now = cfs_rq_clock_task(group_cfs_rq(se));
- if (!__update_entity_runnable_avg(now, &se->avg, se->on_rq,
+ if (!__update_entity_runnable_avg(now, cpu, &se->avg, se->on_rq,
cfs_rq->curr == se))
return;
--
1.9.1
The average running time of RT tasks is used to estimate the remaining compute
capacity for CFS tasks. This remaining capacity is the original capacity scaled
down by a factor (aka scale_rt_capacity). This estimation of available capacity
must also be invariant with frequency scaling.
A frequency scaling factor is applied on the running time of the RT tasks for
computing scale_rt_capacity.
In sched_rt_avg_update, we now scale the RT execution time like below:
rq->rt_avg += rt_delta * arch_scale_freq_capacity() >> SCHED_CAPACITY_SHIFT
Then, scale_rt_capacity can be summarized by:
scale_rt_capacity = SCHED_CAPACITY_SCALE * available / total
with available = total - rq->rt_avg
This has been been optimized in current code by
scale_rt_capacity = available / (total >> SCHED_CAPACITY_SHIFT)
But we can also developed the equation like below
scale_rt_capacity = SCHED_CAPACITY_SCALE -
((rq->rt_avg << SCHED_CAPACITY_SHIFT) / total)
and we can optimize the equation by removing SCHED_CAPACITY_SHIFT shift in
the computation of rq->rt_avg and scale_rt_capacity
so rq->rt_avg += rt_delta * arch_scale_freq_capacity()
and
scale_rt_capacity = SCHED_CAPACITY_SCALE - (rq->rt_avg / total)
arch_scale_frequency_capacity will be called in the hot path of the scheduler
which implies to have a short and efficient function.
As an example, arch_scale_frequency_capacity should return a cached value that
is updated periodically outside of the hot path.
Signed-off-by: Vincent Guittot <[email protected]>
Acked-by: Morten Rasmussen <[email protected]>
---
kernel/sched/fair.c | 17 +++++------------
kernel/sched/sched.h | 4 +++-
2 files changed, 8 insertions(+), 13 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7f031e4..dc7c693 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6004,7 +6004,7 @@ unsigned long __weak arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
static unsigned long scale_rt_capacity(int cpu)
{
struct rq *rq = cpu_rq(cpu);
- u64 total, available, age_stamp, avg;
+ u64 total, used, age_stamp, avg;
s64 delta;
/*
@@ -6020,19 +6020,12 @@ static unsigned long scale_rt_capacity(int cpu)
total = sched_avg_period() + delta;
- if (unlikely(total < avg)) {
- /* Ensures that capacity won't end up being negative */
- available = 0;
- } else {
- available = total - avg;
- }
+ used = div_u64(avg, total);
- if (unlikely((s64)total < SCHED_CAPACITY_SCALE))
- total = SCHED_CAPACITY_SCALE;
+ if (likely(used < SCHED_CAPACITY_SCALE))
+ return SCHED_CAPACITY_SCALE - used;
- total >>= SCHED_CAPACITY_SHIFT;
-
- return div_u64(available, total);
+ return 1;
}
static void update_cpu_capacity(struct sched_domain *sd, int cpu)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 65fa7b5..23c6dd7 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1374,9 +1374,11 @@ static inline int hrtick_enabled(struct rq *rq)
#ifdef CONFIG_SMP
extern void sched_avg_update(struct rq *rq);
+extern unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu);
+
static inline void sched_rt_avg_update(struct rq *rq, u64 rt_delta)
{
- rq->rt_avg += rt_delta;
+ rq->rt_avg += rt_delta * arch_scale_freq_capacity(NULL, cpu_of(rq));
sched_avg_update(rq);
}
#else
--
1.9.1
This new field cpu_capacity_orig reflects the original capacity of a CPU
before being altered by rt tasks and/or IRQ
The cpu_capacity_orig will be used:
- to detect when the capacity of a CPU has been noticeably reduced so we can
trig load balance to look for a CPU with better capacity. As an example, we
can detect when a CPU handles a significant amount of irq
(with CONFIG_IRQ_TIME_ACCOUNTING) but this CPU is seen as an idle CPU by
scheduler whereas CPUs, which are really idle, are available.
- evaluate the available capacity for CFS tasks
Signed-off-by: Vincent Guittot <[email protected]>
Reviewed-by: Kamalesh Babulal <[email protected]>
Acked-by: Morten Rasmussen <[email protected]>
---
kernel/sched/core.c | 2 +-
kernel/sched/fair.c | 8 +++++++-
kernel/sched/sched.h | 1 +
3 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 97fe79c..28e3ec2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7216,7 +7216,7 @@ void __init sched_init(void)
#ifdef CONFIG_SMP
rq->sd = NULL;
rq->rd = NULL;
- rq->cpu_capacity = SCHED_CAPACITY_SCALE;
+ rq->cpu_capacity = rq->cpu_capacity_orig = SCHED_CAPACITY_SCALE;
rq->post_schedule = 0;
rq->active_balance = 0;
rq->next_balance = jiffies;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index dc7c693..10f84c3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4363,6 +4363,11 @@ static unsigned long capacity_of(int cpu)
return cpu_rq(cpu)->cpu_capacity;
}
+static unsigned long capacity_orig_of(int cpu)
+{
+ return cpu_rq(cpu)->cpu_capacity_orig;
+}
+
static unsigned long cpu_avg_load_per_task(int cpu)
{
struct rq *rq = cpu_rq(cpu);
@@ -6040,6 +6045,7 @@ static void update_cpu_capacity(struct sched_domain *sd, int cpu)
capacity >>= SCHED_CAPACITY_SHIFT;
+ cpu_rq(cpu)->cpu_capacity_orig = capacity;
sdg->sgc->capacity_orig = capacity;
capacity *= scale_rt_capacity(cpu);
@@ -6094,7 +6100,7 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
* Runtime updates will correct capacity_orig.
*/
if (unlikely(!rq->sd)) {
- capacity_orig += capacity_of(cpu);
+ capacity_orig += capacity_orig_of(cpu);
capacity += capacity_of(cpu);
continue;
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 23c6dd7..9f06d24 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -603,6 +603,7 @@ struct rq {
struct sched_domain *sd;
unsigned long cpu_capacity;
+ unsigned long cpu_capacity_orig;
unsigned char idle_balance;
/* For active balancing */
--
1.9.1
Monitor the usage level of each group of each sched_domain level. The usage is
the portion of cpu_capacity_orig that is currently used on a CPU or group of
CPUs. We use the utilization_load_avg to evaluate the usage level of each
group.
The utilization_load_avg only takes into account the running time of the CFS
tasks on a CPU with a maximum value of SCHED_LOAD_SCALE when the CPU is fully
utilized. Nevertheless, we must cap utilization_load_avg which can be temporaly
greater than SCHED_LOAD_SCALE after the migration of a task on this CPU and
until the metrics are stabilized.
The utilization_load_avg is in the range [0..SCHED_LOAD_SCALE] to reflect the
running load on the CPU whereas the available capacity for the CFS task is in
the range [0..cpu_capacity_orig]. In order to test if a CPU is fully utilized
by CFS tasks, we have to scale the utilization in the cpu_capacity_orig range
of the CPU to get the usage of the latter. The usage can then be compared with
the available capacity (ie cpu_capacity) to deduct the usage level of a CPU.
The frequency scaling invariance of the usage is not taken into account in this
patch, it will be solved in another patch which will deal with frequency
scaling invariance on the running_load_avg.
Signed-off-by: Vincent Guittot <[email protected]>
Acked-by: Morten Rasmussen <[email protected]>
---
kernel/sched/fair.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 10f84c3..faf61a2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4781,6 +4781,33 @@ static int select_idle_sibling(struct task_struct *p, int target)
done:
return target;
}
+/*
+ * get_cpu_usage returns the amount of capacity of a CPU that is used by CFS
+ * tasks. The unit of the return value must capacity so we can compare the
+ * usage with the capacity of the CPU that is available for CFS task (ie
+ * cpu_capacity).
+ * cfs.utilization_load_avg is the sum of running time of runnable tasks on a
+ * CPU. It represents the amount of utilization of a CPU in the range
+ * [0..SCHED_LOAD_SCALE]. The usage of a CPU can't be higher than the full
+ * capacity of the CPU because it's about the running time on this CPU.
+ * Nevertheless, cfs.utilization_load_avg can be higher than SCHED_LOAD_SCALE
+ * because of unfortunate rounding in avg_period and running_load_avg or just
+ * after migrating tasks until the average stabilizes with the new running
+ * time. So we need to check that the usage stays into the range
+ * [0..cpu_capacity_orig] and cap if necessary.
+ * Without capping the usage, a group could be seen as overloaded (CPU0 usage
+ * at 121% + CPU1 usage at 80%) whereas CPU1 has 20% of available capacity/
+ */
+static int get_cpu_usage(int cpu)
+{
+ unsigned long usage = cpu_rq(cpu)->cfs.utilization_load_avg;
+ unsigned long capacity = capacity_orig_of(cpu);
+
+ if (usage >= SCHED_LOAD_SCALE)
+ return capacity;
+
+ return (usage * capacity) >> SCHED_LOAD_SHIFT;
+}
/*
* select_task_rq_fair: Select target runqueue for the waking task in domains
@@ -5907,6 +5934,7 @@ struct sg_lb_stats {
unsigned long sum_weighted_load; /* Weighted load of group's tasks */
unsigned long load_per_task;
unsigned long group_capacity;
+ unsigned long group_usage; /* Total usage of the group */
unsigned int sum_nr_running; /* Nr tasks running in the group */
unsigned int group_capacity_factor;
unsigned int idle_cpus;
@@ -6255,6 +6283,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
load = source_load(i, load_idx);
sgs->group_load += load;
+ sgs->group_usage += get_cpu_usage(i);
sgs->sum_nr_running += rq->cfs.h_nr_running;
if (rq->nr_running > 1)
--
1.9.1
The scheduler tries to compute how many tasks a group of CPUs can handle by
assuming that a task's load is SCHED_LOAD_SCALE and a CPU's capacity is
SCHED_CAPACITY_SCALE. group_capacity_factor divides the capacity of the group
by SCHED_LOAD_SCALE to estimate how many task can run in the group. Then, it
compares this value with the sum of nr_running to decide if the group is
overloaded or not. But the group_capacity_factor is hardly working for SMT
system, it sometimes works for big cores but fails to do the right thing for
little cores.
Below are two examples to illustrate the problem that this patch solves:
1- If the original capacity of a CPU is less than SCHED_CAPACITY_SCALE
(640 as an example), a group of 3 CPUS will have a max capacity_factor of 2
(div_round_closest(3x640/1024) = 2) which means that it will be seen as
overloaded even if we have only one task per CPU.
2 - If the original capacity of a CPU is greater than SCHED_CAPACITY_SCALE
(1512 as an example), a group of 4 CPUs will have a capacity_factor of 4
(at max and thanks to the fix [0] for SMT system that prevent the apparition
of ghost CPUs) but if one CPU is fully used by rt tasks (and its capacity is
reduced to nearly nothing), the capacity factor of the group will still be 4
(div_round_closest(3*1512/1024) = 5 which is cap to 4 with [0]).
So, this patch tries to solve this issue by removing capacity_factor and
replacing it with the 2 following metrics :
-The available CPU's capacity for CFS tasks which is already used by
load_balance.
-The usage of the CPU by the CFS tasks. For the latter, utilization_avg_contrib
has been re-introduced to compute the usage of a CPU by CFS tasks.
group_capacity_factor and group_has_free_capacity has been removed and replaced
by group_no_capacity. We compare the number of task with the number of CPUs and
we evaluate the level of utilization of the CPUs to define if a group is
overloaded or if a group has capacity to handle more tasks.
For SD_PREFER_SIBLING, a group is tagged overloaded if it has more than 1 task
so it will be selected in priority (among the overloaded groups). Since [1],
SD_PREFER_SIBLING is no more concerned by the computation of load_above_capacity
because local is not overloaded.
[1] 9a5d9ba6a363 ("sched/fair: Allow calculate_imbalance() to move idle cpus")
Signed-off-by: Vincent Guittot <[email protected]>
---
kernel/sched/fair.c | 139 +++++++++++++++++++++++++++-------------------------
1 file changed, 72 insertions(+), 67 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index faf61a2..9d7431f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5936,11 +5936,10 @@ struct sg_lb_stats {
unsigned long group_capacity;
unsigned long group_usage; /* Total usage of the group */
unsigned int sum_nr_running; /* Nr tasks running in the group */
- unsigned int group_capacity_factor;
unsigned int idle_cpus;
unsigned int group_weight;
enum group_type group_type;
- int group_has_free_capacity;
+ int group_no_capacity;
#ifdef CONFIG_NUMA_BALANCING
unsigned int nr_numa_running;
unsigned int nr_preferred_running;
@@ -6156,28 +6155,15 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
}
/*
- * Try and fix up capacity for tiny siblings, this is needed when
- * things like SD_ASYM_PACKING need f_b_g to select another sibling
- * which on its own isn't powerful enough.
- *
- * See update_sd_pick_busiest() and check_asym_packing().
+ * Check whether the capacity of the rq has been noticeably reduced by side
+ * activity. The imbalance_pct is used for the threshold.
+ * Return true is the capacity is reduced
*/
static inline int
-fix_small_capacity(struct sched_domain *sd, struct sched_group *group)
+check_cpu_capacity(struct rq *rq, struct sched_domain *sd)
{
- /*
- * Only siblings can have significantly less than SCHED_CAPACITY_SCALE
- */
- if (!(sd->flags & SD_SHARE_CPUCAPACITY))
- return 0;
-
- /*
- * If ~90% of the cpu_capacity is still there, we're good.
- */
- if (group->sgc->capacity * 32 > group->sgc->capacity_orig * 29)
- return 1;
-
- return 0;
+ return ((rq->cpu_capacity * sd->imbalance_pct) <
+ (rq->cpu_capacity_orig * 100));
}
/*
@@ -6215,37 +6201,56 @@ static inline int sg_imbalanced(struct sched_group *group)
}
/*
- * Compute the group capacity factor.
- *
- * Avoid the issue where N*frac(smt_capacity) >= 1 creates 'phantom' cores by
- * first dividing out the smt factor and computing the actual number of cores
- * and limit unit capacity with that.
+ * group_has_capacity returns true if the group has spare capacity that could
+ * be used by some tasks.
+ * We consider that a group has spare capacity if the * number of task is
+ * smaller than the number of CPUs or if the usage is lower than the available
+ * capacity for CFS tasks.
+ * For the latter, we use a threshold to stabilize the state, to take into
+ * account the variance of the tasks' load and to return true if the available
+ * capacity in meaningful for the load balancer.
+ * As an example, an available capacity of 1% can appear but it doesn't make
+ * any benefit for the load balance.
*/
-static inline int sg_capacity_factor(struct lb_env *env, struct sched_group *group)
+static inline bool
+group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs)
{
- unsigned int capacity_factor, smt, cpus;
- unsigned int capacity, capacity_orig;
+ if (sgs->sum_nr_running < sgs->group_weight)
+ return true;
- capacity = group->sgc->capacity;
- capacity_orig = group->sgc->capacity_orig;
- cpus = group->group_weight;
+ if ((sgs->group_capacity * 100) >
+ (sgs->group_usage * env->sd->imbalance_pct))
+ return true;
- /* smt := ceil(cpus / capacity), assumes: 1 < smt_capacity < 2 */
- smt = DIV_ROUND_UP(SCHED_CAPACITY_SCALE * cpus, capacity_orig);
- capacity_factor = cpus / smt; /* cores */
+ return false;
+}
+
+/*
+ * group_is_overloaded returns true if the group has more tasks than it can
+ * handle.
+ * group_is_overloaded is not equals to !group_has_capacity because a group
+ * with the exact right number of tasks, has no more spare capacity but is not
+ * overloaded so both group_has_capacity and group_is_overloaded return
+ * false.
+ */
+static inline bool
+group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs)
+{
+ if (sgs->sum_nr_running <= sgs->group_weight)
+ return false;
- capacity_factor = min_t(unsigned,
- capacity_factor, DIV_ROUND_CLOSEST(capacity, SCHED_CAPACITY_SCALE));
- if (!capacity_factor)
- capacity_factor = fix_small_capacity(env->sd, group);
+ if ((sgs->group_capacity * 100) <
+ (sgs->group_usage * env->sd->imbalance_pct))
+ return true;
- return capacity_factor;
+ return false;
}
-static enum group_type
-group_classify(struct sched_group *group, struct sg_lb_stats *sgs)
+static enum group_type group_classify(struct lb_env *env,
+ struct sched_group *group,
+ struct sg_lb_stats *sgs)
{
- if (sgs->sum_nr_running > sgs->group_capacity_factor)
+ if (sgs->group_no_capacity)
return group_overloaded;
if (sg_imbalanced(group))
@@ -6306,11 +6311,9 @@ static inline void update_sg_lb_stats(struct lb_env *env,
sgs->load_per_task = sgs->sum_weighted_load / sgs->sum_nr_running;
sgs->group_weight = group->group_weight;
- sgs->group_capacity_factor = sg_capacity_factor(env, group);
- sgs->group_type = group_classify(group, sgs);
- if (sgs->group_capacity_factor > sgs->sum_nr_running)
- sgs->group_has_free_capacity = 1;
+ sgs->group_no_capacity = group_is_overloaded(env, sgs);
+ sgs->group_type = group_classify(env, group, sgs);
}
/**
@@ -6432,18 +6435,19 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
/*
* In case the child domain prefers tasks go to siblings
- * first, lower the sg capacity factor to one so that we'll try
+ * first, lower the sg capacity so that we'll try
* and move all the excess tasks away. We lower the capacity
* of a group only if the local group has the capacity to fit
- * these excess tasks, i.e. nr_running < group_capacity_factor. The
- * extra check prevents the case where you always pull from the
- * heaviest group when it is already under-utilized (possible
- * with a large weight task outweighs the tasks on the system).
+ * these excess tasks. The extra check prevents the case where
+ * you always pull from the heaviest group when it is already
+ * under-utilized (possible with a large weight task outweighs
+ * the tasks on the system).
*/
if (prefer_sibling && sds->local &&
- sds->local_stat.group_has_free_capacity) {
- sgs->group_capacity_factor = min(sgs->group_capacity_factor, 1U);
- sgs->group_type = group_classify(sg, sgs);
+ group_has_capacity(env, &sds->local_stat) &&
+ (sgs->sum_nr_running > 1)) {
+ sgs->group_no_capacity = 1;
+ sgs->group_type = group_overloaded;
}
if (update_sd_pick_busiest(env, sds, sg, sgs)) {
@@ -6623,11 +6627,12 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
*/
if (busiest->group_type == group_overloaded &&
local->group_type == group_overloaded) {
- load_above_capacity =
- (busiest->sum_nr_running - busiest->group_capacity_factor);
-
- load_above_capacity *= (SCHED_LOAD_SCALE * SCHED_CAPACITY_SCALE);
- load_above_capacity /= busiest->group_capacity;
+ load_above_capacity = busiest->sum_nr_running *
+ SCHED_LOAD_SCALE;
+ if (load_above_capacity > busiest->group_capacity)
+ load_above_capacity -= busiest->group_capacity;
+ else
+ load_above_capacity = ~0UL;
}
/*
@@ -6690,6 +6695,7 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
local = &sds.local_stat;
busiest = &sds.busiest_stat;
+ /* ASYM feature bypasses nice load balance check */
if ((env->idle == CPU_IDLE || env->idle == CPU_NEWLY_IDLE) &&
check_asym_packing(env, &sds))
return sds.busiest;
@@ -6710,8 +6716,8 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
goto force_balance;
/* SD_BALANCE_NEWIDLE trumps SMP nice when underutilized */
- if (env->idle == CPU_NEWLY_IDLE && local->group_has_free_capacity &&
- !busiest->group_has_free_capacity)
+ if (env->idle == CPU_NEWLY_IDLE && group_has_capacity(env, local) &&
+ busiest->group_no_capacity)
goto force_balance;
/*
@@ -6770,7 +6776,7 @@ static struct rq *find_busiest_queue(struct lb_env *env,
int i;
for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
- unsigned long capacity, capacity_factor, wl;
+ unsigned long capacity, wl;
enum fbq_type rt;
rq = cpu_rq(i);
@@ -6799,9 +6805,6 @@ static struct rq *find_busiest_queue(struct lb_env *env,
continue;
capacity = capacity_of(i);
- capacity_factor = DIV_ROUND_CLOSEST(capacity, SCHED_CAPACITY_SCALE);
- if (!capacity_factor)
- capacity_factor = fix_small_capacity(env->sd, group);
wl = weighted_cpuload(i);
@@ -6809,7 +6812,9 @@ static struct rq *find_busiest_queue(struct lb_env *env,
* When comparing with imbalance, use weighted_cpuload()
* which is not scaled with the cpu capacity.
*/
- if (capacity_factor && rq->nr_running == 1 && wl > env->imbalance)
+
+ if (rq->nr_running == 1 && wl > env->imbalance &&
+ !check_cpu_capacity(rq, env->sd))
continue;
/*
--
1.9.1
Signed-off-by: Vincent Guittot <[email protected]>
---
kernel/sched/core.c | 12 ------------
kernel/sched/fair.c | 13 +++----------
kernel/sched/sched.h | 2 +-
3 files changed, 4 insertions(+), 23 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 28e3ec2..29f7037 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5446,17 +5446,6 @@ static int sched_domain_debug_one(struct sched_domain *sd, int cpu, int level,
break;
}
- /*
- * Even though we initialize ->capacity to something semi-sane,
- * we leave capacity_orig unset. This allows us to detect if
- * domain iteration is still funny without causing /0 traps.
- */
- if (!group->sgc->capacity_orig) {
- printk(KERN_CONT "\n");
- printk(KERN_ERR "ERROR: domain->cpu_capacity not set\n");
- break;
- }
-
if (!cpumask_weight(sched_group_cpus(group))) {
printk(KERN_CONT "\n");
printk(KERN_ERR "ERROR: empty group\n");
@@ -5941,7 +5930,6 @@ build_overlap_sched_groups(struct sched_domain *sd, int cpu)
* die on a /0 trap.
*/
sg->sgc->capacity = SCHED_CAPACITY_SCALE * cpumask_weight(sg_span);
- sg->sgc->capacity_orig = sg->sgc->capacity;
/*
* Make sure the first group of this domain contains the
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9d7431f..7420d21 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6073,7 +6073,6 @@ static void update_cpu_capacity(struct sched_domain *sd, int cpu)
capacity >>= SCHED_CAPACITY_SHIFT;
cpu_rq(cpu)->cpu_capacity_orig = capacity;
- sdg->sgc->capacity_orig = capacity;
capacity *= scale_rt_capacity(cpu);
capacity >>= SCHED_CAPACITY_SHIFT;
@@ -6089,7 +6088,7 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
{
struct sched_domain *child = sd->child;
struct sched_group *group, *sdg = sd->groups;
- unsigned long capacity, capacity_orig;
+ unsigned long capacity;
unsigned long interval;
interval = msecs_to_jiffies(sd->balance_interval);
@@ -6101,7 +6100,7 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
return;
}
- capacity_orig = capacity = 0;
+ capacity = 0;
if (child->flags & SD_OVERLAP) {
/*
@@ -6121,19 +6120,15 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
* Use capacity_of(), which is set irrespective of domains
* in update_cpu_capacity().
*
- * This avoids capacity/capacity_orig from being 0 and
+ * This avoids capacity from being 0 and
* causing divide-by-zero issues on boot.
- *
- * Runtime updates will correct capacity_orig.
*/
if (unlikely(!rq->sd)) {
- capacity_orig += capacity_orig_of(cpu);
capacity += capacity_of(cpu);
continue;
}
sgc = rq->sd->groups->sgc;
- capacity_orig += sgc->capacity_orig;
capacity += sgc->capacity;
}
} else {
@@ -6144,13 +6139,11 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
group = child->groups;
do {
- capacity_orig += group->sgc->capacity_orig;
capacity += group->sgc->capacity;
group = group->next;
} while (group != child->groups);
}
- sdg->sgc->capacity_orig = capacity_orig;
sdg->sgc->capacity = capacity;
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 9f06d24..24c4aaf 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -814,7 +814,7 @@ struct sched_group_capacity {
* CPU capacity of this group, SCHED_LOAD_SCALE being max capacity
* for a single CPU.
*/
- unsigned int capacity, capacity_orig;
+ unsigned int capacity;
unsigned long next_update;
int imbalance; /* XXX unrelated to capacity but shared group state */
/*
--
1.9.1
Add the SD_PREFER_SIBLING flag for SMT level in order to ensure that
the scheduler will put at least 1 task per core.
Signed-off-by: Vincent Guittot <[email protected]>
Reviewed-by: Preeti U. Murthy <[email protected]>
---
kernel/sched/core.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 29f7037..753f0a2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6240,6 +6240,7 @@ sd_init(struct sched_domain_topology_level *tl, int cpu)
*/
if (sd->flags & SD_SHARE_CPUCAPACITY) {
+ sd->flags |= SD_PREFER_SIBLING;
sd->imbalance_pct = 110;
sd->smt_gain = 1178; /* ~15% */
--
1.9.1
When a CPU is used to handle a lot of IRQs or some RT tasks, the remaining
capacity for CFS tasks can be significantly reduced. Once we detect such
situation by comparing cpu_capacity_orig and cpu_capacity, we trig an idle
load balance to check if it's worth moving its tasks on an idle CPU.
It's worth trying to move the task before the CPU is fully utilized to
minimize the preemption by irq or RT tasks.
Once the idle load_balance has selected the busiest CPU, it will look for an
active load balance for only two cases :
- there is only 1 task on the busiest CPU.
- we haven't been able to move a task of the busiest rq.
A CPU with a reduced capacity is included in the 1st case, and it's worth to
actively migrate its task if the idle CPU has got more available capacity for
CFS tasks. This test has been added in need_active_balance.
As a sidenote, this will not generate more spurious ilb because we already
trig an ilb if there is more than 1 busy cpu. If this cpu is the only one that
has a task, we will trig the ilb once for migrating the task.
The nohz_kick_needed function has been cleaned up a bit while adding the new
test
env.src_cpu and env.src_rq must be set unconditionnally because they are used
in need_active_balance which is called even if busiest->nr_running equals 1
Signed-off-by: Vincent Guittot <[email protected]>
---
kernel/sched/fair.c | 69 ++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 47 insertions(+), 22 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7420d21..e70c315 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6855,6 +6855,19 @@ static int need_active_balance(struct lb_env *env)
return 1;
}
+ /*
+ * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.
+ * It's worth migrating the task if the src_cpu's capacity is reduced
+ * because of other sched_class or IRQs if more capacity stays
+ * available on dst_cpu.
+ */
+ if ((env->idle != CPU_NOT_IDLE) &&
+ (env->src_rq->cfs.h_nr_running == 1)) {
+ if ((check_cpu_capacity(env->src_rq, sd)) &&
+ (capacity_of(env->src_cpu)*sd->imbalance_pct < capacity_of(env->dst_cpu)*100))
+ return 1;
+ }
+
return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);
}
@@ -6954,6 +6967,9 @@ static int load_balance(int this_cpu, struct rq *this_rq,
schedstat_add(sd, lb_imbalance[idle], env.imbalance);
+ env.src_cpu = busiest->cpu;
+ env.src_rq = busiest;
+
ld_moved = 0;
if (busiest->nr_running > 1) {
/*
@@ -6963,8 +6979,6 @@ static int load_balance(int this_cpu, struct rq *this_rq,
* correctly treated as an imbalance.
*/
env.flags |= LBF_ALL_PINNED;
- env.src_cpu = busiest->cpu;
- env.src_rq = busiest;
env.loop_max = min(sysctl_sched_nr_migrate, busiest->nr_running);
more_balance:
@@ -7664,22 +7678,25 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
/*
* Current heuristic for kicking the idle load balancer in the presence
- * of an idle cpu is the system.
+ * of an idle cpu in the system.
* - This rq has more than one task.
- * - At any scheduler domain level, this cpu's scheduler group has multiple
- * busy cpu's exceeding the group's capacity.
+ * - This rq has at least one CFS task and the capacity of the CPU is
+ * significantly reduced because of RT tasks or IRQs.
+ * - At parent of LLC scheduler domain level, this cpu's scheduler group has
+ * multiple busy cpu.
* - For SD_ASYM_PACKING, if the lower numbered cpu's in the scheduler
* domain span are idle.
*/
-static inline int nohz_kick_needed(struct rq *rq)
+static inline bool nohz_kick_needed(struct rq *rq)
{
unsigned long now = jiffies;
struct sched_domain *sd;
struct sched_group_capacity *sgc;
int nr_busy, cpu = rq->cpu;
+ bool kick = false;
if (unlikely(rq->idle_balance))
- return 0;
+ return false;
/*
* We may be recently in ticked or tickless idle mode. At the first
@@ -7693,38 +7710,46 @@ static inline int nohz_kick_needed(struct rq *rq)
* balancing.
*/
if (likely(!atomic_read(&nohz.nr_cpus)))
- return 0;
+ return false;
if (time_before(now, nohz.next_balance))
- return 0;
+ return false;
if (rq->nr_running >= 2)
- goto need_kick;
+ return true;
rcu_read_lock();
sd = rcu_dereference(per_cpu(sd_busy, cpu));
-
if (sd) {
sgc = sd->groups->sgc;
nr_busy = atomic_read(&sgc->nr_busy_cpus);
- if (nr_busy > 1)
- goto need_kick_unlock;
+ if (nr_busy > 1) {
+ kick = true;
+ goto unlock;
+ }
+
}
- sd = rcu_dereference(per_cpu(sd_asym, cpu));
+ sd = rcu_dereference(rq->sd);
+ if (sd) {
+ if ((rq->cfs.h_nr_running >= 1) &&
+ check_cpu_capacity(rq, sd)) {
+ kick = true;
+ goto unlock;
+ }
+ }
+ sd = rcu_dereference(per_cpu(sd_asym, cpu));
if (sd && (cpumask_first_and(nohz.idle_cpus_mask,
- sched_domain_span(sd)) < cpu))
- goto need_kick_unlock;
-
- rcu_read_unlock();
- return 0;
+ sched_domain_span(sd)) < cpu)) {
+ kick = true;
+ goto unlock;
+ }
-need_kick_unlock:
+unlock:
rcu_read_unlock();
-need_kick:
- return 1;
+ return kick;
}
#else
static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { }
--
1.9.1
On 1 April 2015 at 05:37, Xunlei Pang <[email protected]> wrote:
> Hi Vincent,
>
> On 27 March 2015 at 23:59, Vincent Guittot <[email protected]> wrote:
>> On 27 March 2015 at 15:52, Xunlei Pang <[email protected]> wrote:
>>> Hi Vincent,
>>>
>>> On 27 February 2015 at 23:54, Vincent Guittot
>>> <[email protected]> wrote:
>>>> /**
>>>> @@ -6432,18 +6435,19 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
>>>>
>>>> /*
>>>> * In case the child domain prefers tasks go to siblings
>>>> - * first, lower the sg capacity factor to one so that we'll try
>>>> + * first, lower the sg capacity so that we'll try
>>>> * and move all the excess tasks away. We lower the capacity
>>>> * of a group only if the local group has the capacity to fit
>>>> - * these excess tasks, i.e. nr_running < group_capacity_factor. The
>>>> - * extra check prevents the case where you always pull from the
>>>> - * heaviest group when it is already under-utilized (possible
>>>> - * with a large weight task outweighs the tasks on the system).
>>>> + * these excess tasks. The extra check prevents the case where
>>>> + * you always pull from the heaviest group when it is already
>>>> + * under-utilized (possible with a large weight task outweighs
>>>> + * the tasks on the system).
>>>> */
>>>> if (prefer_sibling && sds->local &&
>>>> - sds->local_stat.group_has_free_capacity) {
>>>> - sgs->group_capacity_factor = min(sgs->group_capacity_factor, 1U);
>>>> - sgs->group_type = group_classify(sg, sgs);
>>>> + group_has_capacity(env, &sds->local_stat) &&
>>>> + (sgs->sum_nr_running > 1)) {
>>>> + sgs->group_no_capacity = 1;
>>>> + sgs->group_type = group_overloaded;
>>>> }
>>>>
>>>
>>> For SD_PREFER_SIBLING, if local has 1 task and group_has_capacity()
>>> returns true(but not overloaded) for it, and assume sgs group has 2
>>> tasks, should we still mark this group overloaded?
>>
>> yes, the load balance will then choose if it's worth pulling it or not
>> depending of the load of each groups
>
> Maybe I didn't make it clearly.
> For example, CPU0~1 are SMT siblings, CPU2~CPU3 are another pair.
> CPU0 is idle, others each has 1 task. Then according to this patch,
> CPU2~CPU3(as one group) will be viewed as overloaded(CPU0~CPU1 as
> local group, and group_has_capacity() returns true here), so the
> balancer may initiate an active task moving. This is different from
> the current code as SD_PREFER_SIBLING logic does. Is this problematic?
IMHO, it's not problematic, It's worth triggering a load balance if
there is an imbalance between the 2 groups (as an example CPU0~1 has
one low nice prio task but CPU1~2 have 2 high nice prio tasks) so the
decision will be done when calculating the imbalance
Vincent
>
>>
>>>
>>> -Xunlei
Hi Vincent,
On 1 April 2015 at 17:06, Vincent Guittot <[email protected]> wrote:
> On 1 April 2015 at 05:37, Xunlei Pang <[email protected]> wrote:
>> Hi Vincent,
>>
>> On 27 March 2015 at 23:59, Vincent Guittot <[email protected]> wrote:
>>> On 27 March 2015 at 15:52, Xunlei Pang <[email protected]> wrote:
>>>> Hi Vincent,
>>>>
>>>> On 27 February 2015 at 23:54, Vincent Guittot
>>>> <[email protected]> wrote:
>>>>> /**
>>>>> @@ -6432,18 +6435,19 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
>>>>>
>>>>> /*
>>>>> * In case the child domain prefers tasks go to siblings
>>>>> - * first, lower the sg capacity factor to one so that we'll try
>>>>> + * first, lower the sg capacity so that we'll try
>>>>> * and move all the excess tasks away. We lower the capacity
>>>>> * of a group only if the local group has the capacity to fit
>>>>> - * these excess tasks, i.e. nr_running < group_capacity_factor. The
>>>>> - * extra check prevents the case where you always pull from the
>>>>> - * heaviest group when it is already under-utilized (possible
>>>>> - * with a large weight task outweighs the tasks on the system).
>>>>> + * these excess tasks. The extra check prevents the case where
>>>>> + * you always pull from the heaviest group when it is already
>>>>> + * under-utilized (possible with a large weight task outweighs
>>>>> + * the tasks on the system).
>>>>> */
>>>>> if (prefer_sibling && sds->local &&
>>>>> - sds->local_stat.group_has_free_capacity) {
>>>>> - sgs->group_capacity_factor = min(sgs->group_capacity_factor, 1U);
>>>>> - sgs->group_type = group_classify(sg, sgs);
>>>>> + group_has_capacity(env, &sds->local_stat) &&
>>>>> + (sgs->sum_nr_running > 1)) {
>>>>> + sgs->group_no_capacity = 1;
>>>>> + sgs->group_type = group_overloaded;
>>>>> }
>>>>>
>>>>
>>>> For SD_PREFER_SIBLING, if local has 1 task and group_has_capacity()
>>>> returns true(but not overloaded) for it, and assume sgs group has 2
>>>> tasks, should we still mark this group overloaded?
>>>
>>> yes, the load balance will then choose if it's worth pulling it or not
>>> depending of the load of each groups
>>
>> Maybe I didn't make it clearly.
>> For example, CPU0~1 are SMT siblings, CPU2~CPU3 are another pair.
>> CPU0 is idle, others each has 1 task. Then according to this patch,
>> CPU2~CPU3(as one group) will be viewed as overloaded(CPU0~CPU1 as
>> local group, and group_has_capacity() returns true here), so the
>> balancer may initiate an active task moving. This is different from
>> the current code as SD_PREFER_SIBLING logic does. Is this problematic?
>
> IMHO, it's not problematic, It's worth triggering a load balance if
> there is an imbalance between the 2 groups (as an example CPU0~1 has
> one low nice prio task but CPU1~2 have 2 high nice prio tasks) so the
> decision will be done when calculating the imbalance
Yes, but assuming the balancer calculated some imbalance, after moving
like CPU0~CPU1 have 1 low prio task and 1 high prio task, CPU2~CPU3
have 1 high piro task, seems it does no good because there's only 1
task per CPU after all.
So, is code below better( we may have more than 2 SMT siblings, like
Broadcom XLP processor having 4 SMT per core)?
if (prefer_sibling && sds->local &&
group_has_capacity(env, &sds->local_stat) &&
(sgs->sum_nr_running > sds->local_stat.sum_nr_running + 1)) {
sgs->group_no_capacity = 1;
sgs->group_type = group_overloaded;
}
Thanks,
-Xunlei
On 1 April 2015 at 16:54, Xunlei Pang <[email protected]> wrote:
> Hi Vincent,
>
> On 1 April 2015 at 17:06, Vincent Guittot <[email protected]> wrote:
>> On 1 April 2015 at 05:37, Xunlei Pang <[email protected]> wrote:
>>> Hi Vincent,
>>>
>>> On 27 March 2015 at 23:59, Vincent Guittot <[email protected]> wrote:
>>>> On 27 March 2015 at 15:52, Xunlei Pang <[email protected]> wrote:
>>>>> Hi Vincent,
>>>>>
>>>>> On 27 February 2015 at 23:54, Vincent Guittot
>>>>> <[email protected]> wrote:
>>>>>> /**
>>>>>> @@ -6432,18 +6435,19 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
>>>>>>
>>>>>> /*
>>>>>> * In case the child domain prefers tasks go to siblings
>>>>>> - * first, lower the sg capacity factor to one so that we'll try
>>>>>> + * first, lower the sg capacity so that we'll try
>>>>>> * and move all the excess tasks away. We lower the capacity
>>>>>> * of a group only if the local group has the capacity to fit
>>>>>> - * these excess tasks, i.e. nr_running < group_capacity_factor. The
>>>>>> - * extra check prevents the case where you always pull from the
>>>>>> - * heaviest group when it is already under-utilized (possible
>>>>>> - * with a large weight task outweighs the tasks on the system).
>>>>>> + * these excess tasks. The extra check prevents the case where
>>>>>> + * you always pull from the heaviest group when it is already
>>>>>> + * under-utilized (possible with a large weight task outweighs
>>>>>> + * the tasks on the system).
>>>>>> */
>>>>>> if (prefer_sibling && sds->local &&
>>>>>> - sds->local_stat.group_has_free_capacity) {
>>>>>> - sgs->group_capacity_factor = min(sgs->group_capacity_factor, 1U);
>>>>>> - sgs->group_type = group_classify(sg, sgs);
>>>>>> + group_has_capacity(env, &sds->local_stat) &&
>>>>>> + (sgs->sum_nr_running > 1)) {
>>>>>> + sgs->group_no_capacity = 1;
>>>>>> + sgs->group_type = group_overloaded;
>>>>>> }
>>>>>>
>>>>>
>>>>> For SD_PREFER_SIBLING, if local has 1 task and group_has_capacity()
>>>>> returns true(but not overloaded) for it, and assume sgs group has 2
>>>>> tasks, should we still mark this group overloaded?
>>>>
>>>> yes, the load balance will then choose if it's worth pulling it or not
>>>> depending of the load of each groups
>>>
>>> Maybe I didn't make it clearly.
>>> For example, CPU0~1 are SMT siblings, CPU2~CPU3 are another pair.
>>> CPU0 is idle, others each has 1 task. Then according to this patch,
>>> CPU2~CPU3(as one group) will be viewed as overloaded(CPU0~CPU1 as
>>> local group, and group_has_capacity() returns true here), so the
>>> balancer may initiate an active task moving. This is different from
>>> the current code as SD_PREFER_SIBLING logic does. Is this problematic?
>>
>> IMHO, it's not problematic, It's worth triggering a load balance if
>> there is an imbalance between the 2 groups (as an example CPU0~1 has
>> one low nice prio task but CPU1~2 have 2 high nice prio tasks) so the
>> decision will be done when calculating the imbalance
>
> Yes, but assuming the balancer calculated some imbalance, after moving
> like CPU0~CPU1 have 1 low prio task and 1 high prio task, CPU2~CPU3
> have 1 high piro task, seems it does no good because there's only 1
> task per CPU after all.
In this condition i agree that it doesn't worth to move a task and the
scheduler should not because the imbalance will be too small to found
a busiest queue.
So the decision is more linked to the weighted load of the tasks than
to the number of tasks
>
> So, is code below better( we may have more than 2 SMT siblings, like
> Broadcom XLP processor having 4 SMT per core)?
> if (prefer_sibling && sds->local &&
> group_has_capacity(env, &sds->local_stat) &&
> (sgs->sum_nr_running > sds->local_stat.sum_nr_running + 1)) {
> sgs->group_no_capacity = 1;
> sgs->group_type = group_overloaded;
> }
I would say no because it mainly depends of the weighted load of the
tasks so calculate_imbalance is the right place
Vincent
>
> Thanks,
> -Xunlei
Hi Vincent,
On Fri, Feb 27, 2015 at 04:54:03PM +0100, Vincent Guittot wrote:
>This patchset consolidates several changes in the capacity and the usage
>tracking of the CPU. It provides a frequency invariant metric of the usage of
>CPUs and generally improves the accuracy of load/usage tracking in the
>scheduler. The frequency invariant metric is the foundation required for the
>consolidation of cpufreq and implementation of a fully invariant load tracking.
>These are currently WIP and require several changes to the load balancer
>(including how it will use and interprets load and capacity metrics) and
>extensive validation. The frequency invariance is done with
>arch_scale_freq_capacity and this patchset doesn't provide the backends of
>the function which are architecture dependent.
>
>As discussed at LPC14, Morten and I have consolidated our changes into a single
>patchset to make it easier to review and merge.
>
>During load balance, the scheduler evaluates the number of tasks that a group
>of CPUs can handle. The current method assumes that tasks have a fix load of
>SCHED_LOAD_SCALE and CPUs have a default capacity of SCHED_CAPACITY_SCALE.
>This assumption generates wrong decision by creating ghost cores or by
>removing real ones when the original capacity of CPUs is different from the
>default SCHED_CAPACITY_SCALE. With this patch set, we don't try anymore to
>evaluate the number of available cores based on the group_capacity but instead
>we evaluate the usage of a group and compare it with its capacity.
>
>This patchset mainly replaces the old capacity_factor method by a new one and
>keeps the general policy almost unchanged. These new metrics will be also used
>in later patches.
>
>The CPU usage is based on a running time tracking version of the current
>implementation of the load average tracking. I also have a version that is
>based on the new implementation proposal [1] but I haven't provide the patches
>and results as [1] is still under review. I can provide change above [1] to
>change how CPU usage is computed and to adapt to new mecanism.
Is there performance data for this cpu capacity and usage improvement?
Regards,
Wanpeng Li
>
>Change since V9
> - add a dedicated patch for removing unused capacity_orig
> - update some comments and fix typo
> - change the condition for actively migrating task on CPU with higher capacity
>
>Change since V8
> - reorder patches
>
>Change since V7
> - add freq invariance for usage tracking
> - add freq invariance for scale_rt
> - update comments and commits' message
> - fix init of utilization_avg_contrib
> - fix prefer_sibling
>
>Change since V6
> - add group usage tracking
> - fix some commits' messages
> - minor fix like comments and argument order
>
>Change since V5
> - remove patches that have been merged since v5 : patches 01, 02, 03, 04, 05, 07
> - update commit log and add more details on the purpose of the patches
> - fix/remove useless code with the rebase on patchset [2]
> - remove capacity_orig in sched_group_capacity as it is not used
> - move code in the right patch
> - add some helper function to factorize code
>
>Change since V4
> - rebase to manage conflicts with changes in selection of busiest group
>
>Change since V3:
> - add usage_avg_contrib statistic which sums the running time of tasks on a rq
> - use usage_avg_contrib instead of runnable_avg_sum for cpu_utilization
> - fix replacement power by capacity
> - update some comments
>
>Change since V2:
> - rebase on top of capacity renaming
> - fix wake_affine statistic update
> - rework nohz_kick_needed
> - optimize the active migration of a task from CPU with reduced capacity
> - rename group_activity by group_utilization and remove unused total_utilization
> - repair SD_PREFER_SIBLING and use it for SMT level
> - reorder patchset to gather patches with same topics
>
>Change since V1:
> - add 3 fixes
> - correct some commit messages
> - replace capacity computation by activity
> - take into account current cpu capacity
>
>[1] https://lkml.org/lkml/2014/10/10/131
>[2] https://lkml.org/lkml/2014/7/25/589
>
>Morten Rasmussen (2):
> sched: Track group sched_entity usage contributions
> sched: Make sched entity usage tracking scale-invariant
>
>Vincent Guittot (9):
> sched: add utilization_avg_contrib
> sched: remove frequency scaling from cpu_capacity
> sched: make scale_rt invariant with frequency
> sched: add per rq cpu_capacity_orig
> sched: get CPU's usage statistic
> sched: replace capacity_factor by usage
> sched; remove unused capacity_orig from
> sched: add SD_PREFER_SIBLING for SMT level
> sched: move cfs task on a CPU with higher capacity
>
> include/linux/sched.h | 21 ++-
> kernel/sched/core.c | 15 +--
> kernel/sched/debug.c | 12 +-
> kernel/sched/fair.c | 366 +++++++++++++++++++++++++++++++-------------------
> kernel/sched/sched.h | 15 ++-
> 5 files changed, 271 insertions(+), 158 deletions(-)
>
>--
>1.9.1
>
>--
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>Please read the FAQ at http://www.tux.org/lkml/
On 2 April 2015 at 03:47, Wanpeng Li <[email protected]> wrote:
> Hi Vincent,
> On Fri, Feb 27, 2015 at 04:54:03PM +0100, Vincent Guittot wrote:
>>This patchset consolidates several changes in the capacity and the usage
>>tracking of the CPU. It provides a frequency invariant metric of the usage of
>>CPUs and generally improves the accuracy of load/usage tracking in the
>>scheduler. The frequency invariant metric is the foundation required for the
>>consolidation of cpufreq and implementation of a fully invariant load tracking.
>>These are currently WIP and require several changes to the load balancer
>>(including how it will use and interprets load and capacity metrics) and
>>extensive validation. The frequency invariance is done with
>>arch_scale_freq_capacity and this patchset doesn't provide the backends of
>>the function which are architecture dependent.
>>
>>As discussed at LPC14, Morten and I have consolidated our changes into a single
>>patchset to make it easier to review and merge.
>>
>>During load balance, the scheduler evaluates the number of tasks that a group
>>of CPUs can handle. The current method assumes that tasks have a fix load of
>>SCHED_LOAD_SCALE and CPUs have a default capacity of SCHED_CAPACITY_SCALE.
>>This assumption generates wrong decision by creating ghost cores or by
>>removing real ones when the original capacity of CPUs is different from the
>>default SCHED_CAPACITY_SCALE. With this patch set, we don't try anymore to
>>evaluate the number of available cores based on the group_capacity but instead
>>we evaluate the usage of a group and compare it with its capacity.
>>
>>This patchset mainly replaces the old capacity_factor method by a new one and
>>keeps the general policy almost unchanged. These new metrics will be also used
>>in later patches.
>>
>>The CPU usage is based on a running time tracking version of the current
>>implementation of the load average tracking. I also have a version that is
>>based on the new implementation proposal [1] but I haven't provide the patches
>>and results as [1] is still under review. I can provide change above [1] to
>>change how CPU usage is computed and to adapt to new mecanism.
>
> Is there performance data for this cpu capacity and usage improvement?
I don't have data for this version but i have published figures for
previous one.
https://lkml.org/lkml/2014/8/26/288
This patchset consolidates the tracking of CPU usage and capacity for
all kind of arch and use case by improving the detection of overloaded
CPU.
Regarding the perf bench on SMP system which goals is to use all
available CPU and computing capacity , we should not see perf
improvement but we will not see perf regression too.
The difference is noticeable in mid load use case or when rt task or
irq are involved
Regards,
Vincent
>
> Regards,
> Wanpeng Li
>
>>
>>Change since V9
>> - add a dedicated patch for removing unused capacity_orig
>> - update some comments and fix typo
>> - change the condition for actively migrating task on CPU with higher capacity
>>
>>Change since V8
>> - reorder patches
>>
>>Change since V7
>> - add freq invariance for usage tracking
>> - add freq invariance for scale_rt
>> - update comments and commits' message
>> - fix init of utilization_avg_contrib
>> - fix prefer_sibling
>>
>>Change since V6
>> - add group usage tracking
>> - fix some commits' messages
>> - minor fix like comments and argument order
>>
>>Change since V5
>> - remove patches that have been merged since v5 : patches 01, 02, 03, 04, 05, 07
>> - update commit log and add more details on the purpose of the patches
>> - fix/remove useless code with the rebase on patchset [2]
>> - remove capacity_orig in sched_group_capacity as it is not used
>> - move code in the right patch
>> - add some helper function to factorize code
>>
>>Change since V4
>> - rebase to manage conflicts with changes in selection of busiest group
>>
>>Change since V3:
>> - add usage_avg_contrib statistic which sums the running time of tasks on a rq
>> - use usage_avg_contrib instead of runnable_avg_sum for cpu_utilization
>> - fix replacement power by capacity
>> - update some comments
>>
>>Change since V2:
>> - rebase on top of capacity renaming
>> - fix wake_affine statistic update
>> - rework nohz_kick_needed
>> - optimize the active migration of a task from CPU with reduced capacity
>> - rename group_activity by group_utilization and remove unused total_utilization
>> - repair SD_PREFER_SIBLING and use it for SMT level
>> - reorder patchset to gather patches with same topics
>>
>>Change since V1:
>> - add 3 fixes
>> - correct some commit messages
>> - replace capacity computation by activity
>> - take into account current cpu capacity
>>
>>[1] https://lkml.org/lkml/2014/10/10/131
>>[2] https://lkml.org/lkml/2014/7/25/589
>>
>>Morten Rasmussen (2):
>> sched: Track group sched_entity usage contributions
>> sched: Make sched entity usage tracking scale-invariant
>>
>>Vincent Guittot (9):
>> sched: add utilization_avg_contrib
>> sched: remove frequency scaling from cpu_capacity
>> sched: make scale_rt invariant with frequency
>> sched: add per rq cpu_capacity_orig
>> sched: get CPU's usage statistic
>> sched: replace capacity_factor by usage
>> sched; remove unused capacity_orig from
>> sched: add SD_PREFER_SIBLING for SMT level
>> sched: move cfs task on a CPU with higher capacity
>>
>> include/linux/sched.h | 21 ++-
>> kernel/sched/core.c | 15 +--
>> kernel/sched/debug.c | 12 +-
>> kernel/sched/fair.c | 366 +++++++++++++++++++++++++++++++-------------------
>> kernel/sched/sched.h | 15 ++-
>> 5 files changed, 271 insertions(+), 158 deletions(-)
>>
>>--
>>1.9.1
>>
>>--
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>>More majordomo info at http://vger.kernel.org/majordomo-info.html
>>Please read the FAQ at http://www.tux.org/lkml/
On Wed, Mar 25, 2015 at 05:33:09PM +0000, Peter Zijlstra wrote:
> On Tue, Mar 24, 2015 at 11:00:57AM +0100, Vincent Guittot wrote:
> > On 23 March 2015 at 14:19, Peter Zijlstra <[email protected]> wrote:
> > > On Fri, Feb 27, 2015 at 04:54:07PM +0100, Vincent Guittot wrote:
> > >
> > >> + unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu);
> > >
> > >> + sa->running_avg_sum += delta_w * scale_freq
> > >> + >> SCHED_CAPACITY_SHIFT;
> > >
> > > so the only thing that could be improved is somehow making this
> > > multiplication go away when the arch doesn't implement the function.
> > >
> > > But I'm not sure how to do that without #ifdef.
> > >
> > > Maybe a little something like so then... that should make the compiler
> > > get rid of those multiplications unless the arch needs them.
> >
> > yes, it removes useless multiplication when not used by an arch.
> > It also adds a constraint on the arch side which have to define
> > arch_scale_freq_capacity like below:
> >
> > #define arch_scale_freq_capacity xxx_arch_scale_freq_capacity
> > with xxx_arch_scale_freq_capacity an architecture specific function
>
> Yeah, but it not being weak should make that a compile time warn/fail,
> which should be pretty easy to deal with.
Could you enlighten me a bit about how to define the arch specific
implementation without getting into trouble? I'm failing miserably :(
I thought the arm arch-specific topology.h file was a good place to put
the define as it get included in sched.h, so I did a:
#define arch_scale_freq_capacity arm_arch_scale_freq_capacity
However, I have to put a function prototype in the same (or some other
included) header file to avoid doing an implicit function definition.
arch_scale_freq_capacity() takes a struct sched_domain pointer, so I
have to include linux/sched.h which leads to circular dependency between
linux/sched.h and topology.h.
The only way out I can think of to create (or find) a new arch-specific
header file that can include linux/sched.h and be included in
kernel/sched/sched.h and have the define and prototype in there.
I must be missing something?
We can drop the sched_domain pointer as we don't use it, but I'm going
to do the same trick for arch_scale_cpu_capacity() as well which does
require the sd pointer.
Finally, is introducing an ARCH_HAS_SCALE_FREQ_CAPACITY or similar a
complete no go?
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 91c6736..5707fb7 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1388,12 +1388,14 @@ static inline int hrtick_enabled(struct rq *rq)
#ifdef CONFIG_SMP
extern void sched_avg_update(struct rq *rq);
-#ifndef arch_scale_freq_capacity
+#ifndef ARCH_HAS_SCALE_FREQ_CAPACITY
static __always_inline
unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
{
return SCHED_CAPACITY_SCALE;
}
+#else
+extern unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu);
#endif
static inline void sched_rt_avg_update(struct rq *rq, u64 rt_delta)
On Thu, Apr 02, 2015 at 05:53:09PM +0100, Morten Rasmussen wrote:
> Could you enlighten me a bit about how to define the arch specific
> implementation without getting into trouble? I'm failing miserably :(
Hmm, this was not supposed to be difficult.. :/
> I thought the arm arch-specific topology.h file was a good place to put
> the define as it get included in sched.h, so I did a:
>
> #define arch_scale_freq_capacity arm_arch_scale_freq_capacity
>
> However, I have to put a function prototype in the same (or some other
> included) header file to avoid doing an implicit function definition.
> arch_scale_freq_capacity() takes a struct sched_domain pointer, so I
> have to include linux/sched.h which leads to circular dependency between
> linux/sched.h and topology.h.
Why would you have to include linux/sched.h ?
#define arch_scale_freq_capacity arch_scale_freq_capacity
struct sched_domain;
extern unsigned long arch_scale_freq_capacity(struct sched_domain *, int cpu);
Would work from you asm/topology.h, right?
> We can drop the sched_domain pointer as we don't use it, but I'm going
> to do the same trick for arch_scale_cpu_capacity() as well which does
> require the sd pointer.
Sure, dropping that pointer is fine.
> Finally, is introducing an ARCH_HAS_SCALE_FREQ_CAPACITY or similar a
> complete no go?
It seems out of style, I'd have to go look for the email thread, but
this should more or less be the same no?
On Thu, Apr 02, 2015 at 06:32:38PM +0100, Peter Zijlstra wrote:
> On Thu, Apr 02, 2015 at 05:53:09PM +0100, Morten Rasmussen wrote:
> > Could you enlighten me a bit about how to define the arch specific
> > implementation without getting into trouble? I'm failing miserably :(
>
> Hmm, this was not supposed to be difficult.. :/
I wouldn't have thought so, and it turned out not to be...
>
> > I thought the arm arch-specific topology.h file was a good place to put
> > the define as it get included in sched.h, so I did a:
> >
> > #define arch_scale_freq_capacity arm_arch_scale_freq_capacity
> >
> > However, I have to put a function prototype in the same (or some other
> > included) header file to avoid doing an implicit function definition.
> > arch_scale_freq_capacity() takes a struct sched_domain pointer, so I
> > have to include linux/sched.h which leads to circular dependency between
> > linux/sched.h and topology.h.
>
> Why would you have to include linux/sched.h ?
>
> #define arch_scale_freq_capacity arch_scale_freq_capacity
> struct sched_domain;
> extern unsigned long arch_scale_freq_capacity(struct sched_domain *, int cpu);
>
> Would work from you asm/topology.h, right?
Yes, of course, it works fine. It was just me missing the most obvious
solution. No need to include linux/sched.h, 'struct sched_domain;' was
the bit I was missing. Sorry for the noise.
> > We can drop the sched_domain pointer as we don't use it, but I'm going
> > to do the same trick for arch_scale_cpu_capacity() as well which does
> > require the sd pointer.
>
> Sure, dropping that pointer is fine.
>
> > Finally, is introducing an ARCH_HAS_SCALE_FREQ_CAPACITY or similar a
> > complete no go?
>
> It seems out of style, I'd have to go look for the email thread, but
> this should more or less be the same no?
The above works just fine, so no need for that anyway :)