find_energy_efficient() (feec()) will migrate a task to save energy only
if it saves at least 6% of the total energy consumed by the system. This
conservative approach is a problem on a system where a lot of small tasks
create a huge load on the overall: very few of them will be allowed to migrate
to a smaller CPU, wasting a lot of energy. Instead of trying to determine yet
another margin, let's try to remove it.
The first elements of this patch-set are various fixes and improvement that
stabilizes task_util and ensures energy comparison fairness across all CPUs of
the topology. Only once those fixed, we can completely remove the margin and
let feec() aggressively place task and save energy.
This has been validated by two different ways:
First using LISA's eas_behaviour test suite. This is composed of a set of
scenario and verify if the task placement is optimum. No failure have been
observed and it also improved some tests such as Ramp-Down (as the placement
is now more energy oriented) and *ThreeSmall (as no bouncing between clusters
happen anymore).
* Hikey960: 100% PASSED
* DB-845C: 100% PASSED
* RB5: 100% PASSED
Second, using an Android benchmark: PCMark2 on a Pixel4, with a lot of
backports to have a scheduler as close as we can from mainline.
+------------+-----------------+-----------------+
| Test | Perf | Energy [1] |
+------------+-----------------+-----------------+
| Web2 | -0.3% pval 0.03 | -1.8% pval 0.00 |
| Video2 | -0.3% pval 0.13 | -5.6% pval 0.00 |
| Photo2 [2] | -3.8% pval 0.00 | -1% pval 0.00 |
| Writing2 | 0% pval 0.13 | -1% pval 0.00 |
| Data2 | 0% pval 0.8 | -0.43 pval 0.00 |
+------------+-----------------+-----------------+
The margin removal let the kernel make the best use of the Energy Model,
tasks are more likely to be placed where they fit and this saves a
substantial amount of energy, while having a limited impact on performances.
[1] This is an energy estimation based on the CPU activity and the Energy Model
for this device. "All models are wrong but some are useful"; yes, this is an
imperfect estimation that doesn't take into account some idle states and shared
power rails. Nonetheless this is based on the information the kernel has during
runtime and it proves the scheduler can take better decisions based solely on
those data.
[2] This is the only performance impact observed. The debugging of this test
showed no issue with task placement. The better score was solely due to some
critical threads held on better performing CPUs. If a thread needs a higher
capacity CPU, the placement must result from a user input (with e.g. uclamp
min) instead of being artificially held on less efficient CPUs by feec().
Notice also, the experiment didn't use the Android only latency_sensitive
feature which would hide this problem on a real-life device.
v3 -> v4:
- Minor cosmetic changes (Dietmar)
v2 -> v3:
- feec(): introduce energy_env struct (Dietmar)
- PELT migration decay: Only apply when src CPU is idle (Vincent G.)
- PELT migration decay: Do not apply when cfs_rq is throttled
- PELT migration decay: Snapshot the lag at cfs_rq's level
v1 -> v2:
- Fix PELT migration last_update_time (previously root cfs_rq's).
- Add Dietmar's patches to refactor feec()'s CPU loop.
- feec(): renaming busy time functions get_{pd,tsk}_busy_time()
- feec(): pd_cap computation in the first for_each_cpu loop.
- feec(): create get_pd_max_util() function (previously within compute_energy())
- feec(): rename base_energy_pd to base_energy.
Dietmar Eggemann (3):
sched, drivers: Remove max param from
effective_cpu_util()/sched_cpu_util()
sched/fair: Rename select_idle_mask to select_rq_mask
sched/fair: Use the same cpumask per-PD throughout
find_energy_efficient_cpu()
Vincent Donnefort (4):
sched/fair: Provide u64 read for 32-bits arch helper
sched/fair: Decay task PELT values during wakeup migration
sched/fair: Remove task_util from effective utilization in feec()
sched/fair: Remove the energy margin in feec()
drivers/powercap/dtpm_cpu.c | 33 +--
drivers/thermal/cpufreq_cooling.c | 6 +-
include/linux/sched.h | 2 +-
kernel/sched/core.c | 15 +-
kernel/sched/cpufreq_schedutil.c | 5 +-
kernel/sched/fair.c | 385 ++++++++++++++++++------------
kernel/sched/sched.h | 49 +++-
7 files changed, 298 insertions(+), 197 deletions(-)
--
2.25.1
From: Dietmar Eggemann <[email protected]>
The Perf Domain (PD) cpumask (struct em_perf_domain.cpus) stays
invariant after Energy Model creation, i.e. it is not updated after
CPU hotplug operations.
That's why the PD mask is used in conjunction with the cpu_online_mask
(or Sched Domain cpumask). Thereby the cpu_online_mask is fetched
multiple times (in compute_energy()) during a run-queue selection
for a task.
cpu_online_mask may change during this time which can lead to wrong
energy calculations.
To be able to avoid this, use the select_rq_mask per-cpu cpumask to
create a cpumask out of PD cpumask and cpu_online_mask and pass it
through the function calls of the EAS run-queue selection path.
The PD cpumask for max_spare_cap_cpu/compute_prev_delta selection
(find_energy_efficient_cpu()) is now ANDed not only with the SD mask
but also with the cpu_online_mask. This is fine since this cpumask
has to be in syc with the one used for energy computation
(compute_energy()).
An exclusive cpuset setup with at least one asymmetric CPU capacity
island (hence the additional AND with the SD cpumask) is the obvious
exception here.
Signed-off-by: Dietmar Eggemann <[email protected]>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f1e78f6adc98..97eb8afb336c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6694,14 +6694,14 @@ static unsigned long cpu_util_next(int cpu, struct task_struct *p, int dst_cpu)
* task.
*/
static long
-compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
+compute_energy(struct task_struct *p, int dst_cpu, struct cpumask *cpus,
+ struct perf_domain *pd)
{
- struct cpumask *pd_mask = perf_domain_span(pd);
unsigned long max_util = 0, sum_util = 0, cpu_cap;
int cpu;
- cpu_cap = arch_scale_cpu_capacity(cpumask_first(pd_mask));
- cpu_cap -= arch_scale_thermal_pressure(cpumask_first(pd_mask));
+ cpu_cap = arch_scale_cpu_capacity(cpumask_first(cpus));
+ cpu_cap -= arch_scale_thermal_pressure(cpumask_first(cpus));
/*
* The capacity state of CPUs of the current rd can be driven by CPUs
@@ -6712,7 +6712,7 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
* If an entire pd is outside of the current rd, it will not appear in
* its pd list and will not be accounted by compute_energy().
*/
- for_each_cpu_and(cpu, pd_mask, cpu_online_mask) {
+ for_each_cpu(cpu, cpus) {
unsigned long util_freq = cpu_util_next(cpu, p, dst_cpu);
unsigned long cpu_util, util_running = util_freq;
struct task_struct *tsk = NULL;
@@ -6799,6 +6799,7 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
*/
static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
{
+ struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_rq_mask);
unsigned long prev_delta = ULONG_MAX, best_delta = ULONG_MAX;
struct root_domain *rd = cpu_rq(smp_processor_id())->rd;
int cpu, best_energy_cpu = prev_cpu, target = -1;
@@ -6833,7 +6834,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
unsigned long base_energy_pd;
int max_spare_cap_cpu = -1;
- for_each_cpu_and(cpu, perf_domain_span(pd), sched_domain_span(sd)) {
+ cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);
+
+ for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
if (!cpumask_test_cpu(cpu, p->cpus_ptr))
continue;
@@ -6870,12 +6873,12 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
continue;
/* Compute the 'base' energy of the pd, without @p */
- base_energy_pd = compute_energy(p, -1, pd);
+ base_energy_pd = compute_energy(p, -1, cpus, pd);
base_energy += base_energy_pd;
/* Evaluate the energy impact of using prev_cpu. */
if (compute_prev_delta) {
- prev_delta = compute_energy(p, prev_cpu, pd);
+ prev_delta = compute_energy(p, prev_cpu, cpus, pd);
if (prev_delta < base_energy_pd)
goto unlock;
prev_delta -= base_energy_pd;
@@ -6884,7 +6887,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
/* Evaluate the energy impact of using max_spare_cap_cpu. */
if (max_spare_cap_cpu >= 0) {
- cur_delta = compute_energy(p, max_spare_cap_cpu, pd);
+ cur_delta = compute_energy(p, max_spare_cap_cpu, cpus,
+ pd);
if (cur_delta < base_energy_pd)
goto unlock;
cur_delta -= base_energy_pd;
--
2.25.1
Introducing macro helpers u64_u32_{store,load}() to factorize lockless
accesses to u64 variables for 32-bits architectures.
Users are for now cfs_rq.min_vruntime and sched_avg.last_update_time. To
accommodate the later where the copy lies outside of the structure
(cfs_rq.last_udpate_time_copy instead of sched_avg.last_update_time_copy),
use the _copy() version of those helpers.
Those new helpers encapsulate smp_rmb() and smp_wmb() synchronization and
therefore, have a small penalty in set_task_rq_fair() and init_cfs_rq().
Signed-off-by: Vincent Donnefort <[email protected]>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3eba0dcc4962..5dd38c9df0cc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -600,11 +600,8 @@ static void update_min_vruntime(struct cfs_rq *cfs_rq)
}
/* ensure we never gain time by being placed backwards. */
- cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime);
-#ifndef CONFIG_64BIT
- smp_wmb();
- cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
-#endif
+ u64_u32_store(cfs_rq->min_vruntime,
+ max_vruntime(cfs_rq->min_vruntime, vruntime));
}
static inline bool __entity_less(struct rb_node *a, const struct rb_node *b)
@@ -3301,6 +3298,11 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
}
#ifdef CONFIG_SMP
+static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
+{
+ return u64_u32_load_copy(cfs_rq->avg.last_update_time,
+ cfs_rq->last_update_time_copy);
+}
#ifdef CONFIG_FAIR_GROUP_SCHED
/*
* Because list_add_leaf_cfs_rq always places a child cfs_rq on the list
@@ -3411,27 +3413,9 @@ void set_task_rq_fair(struct sched_entity *se,
if (!(se->avg.last_update_time && prev))
return;
-#ifndef CONFIG_64BIT
- {
- u64 p_last_update_time_copy;
- u64 n_last_update_time_copy;
-
- do {
- p_last_update_time_copy = prev->load_last_update_time_copy;
- n_last_update_time_copy = next->load_last_update_time_copy;
-
- smp_rmb();
+ p_last_update_time = cfs_rq_last_update_time(prev);
+ n_last_update_time = cfs_rq_last_update_time(next);
- p_last_update_time = prev->avg.last_update_time;
- n_last_update_time = next->avg.last_update_time;
-
- } while (p_last_update_time != p_last_update_time_copy ||
- n_last_update_time != n_last_update_time_copy);
- }
-#else
- p_last_update_time = prev->avg.last_update_time;
- n_last_update_time = next->avg.last_update_time;
-#endif
__update_load_avg_blocked_se(p_last_update_time, se);
se->avg.last_update_time = n_last_update_time;
}
@@ -3786,8 +3770,9 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
decayed |= __update_load_avg_cfs_rq(now, cfs_rq);
#ifndef CONFIG_64BIT
- smp_wmb();
- cfs_rq->load_last_update_time_copy = sa->last_update_time;
+ u64_u32_store_copy(sa->last_update_time,
+ cfs_rq->last_update_time_copy,
+ sa->last_update_time);
#endif
return decayed;
@@ -3921,27 +3906,6 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
}
}
-#ifndef CONFIG_64BIT
-static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
-{
- u64 last_update_time_copy;
- u64 last_update_time;
-
- do {
- last_update_time_copy = cfs_rq->load_last_update_time_copy;
- smp_rmb();
- last_update_time = cfs_rq->avg.last_update_time;
- } while (last_update_time != last_update_time_copy);
-
- return last_update_time;
-}
-#else
-static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
-{
- return cfs_rq->avg.last_update_time;
-}
-#endif
-
/*
* Synchronize entity load avg of dequeued entity without locking
* the previous rq.
@@ -6991,21 +6955,8 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu)
if (READ_ONCE(p->__state) == TASK_WAKING) {
struct sched_entity *se = &p->se;
struct cfs_rq *cfs_rq = cfs_rq_of(se);
- u64 min_vruntime;
-#ifndef CONFIG_64BIT
- u64 min_vruntime_copy;
-
- do {
- min_vruntime_copy = cfs_rq->min_vruntime_copy;
- smp_rmb();
- min_vruntime = cfs_rq->min_vruntime;
- } while (min_vruntime != min_vruntime_copy);
-#else
- min_vruntime = cfs_rq->min_vruntime;
-#endif
-
- se->vruntime -= min_vruntime;
+ se->vruntime -= u64_u32_load(cfs_rq->min_vruntime);
}
if (p->on_rq == TASK_ON_RQ_MIGRATING) {
@@ -11453,10 +11404,7 @@ static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
void init_cfs_rq(struct cfs_rq *cfs_rq)
{
cfs_rq->tasks_timeline = RB_ROOT_CACHED;
- cfs_rq->min_vruntime = (u64)(-(1LL << 20));
-#ifndef CONFIG_64BIT
- cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
-#endif
+ u64_u32_store(cfs_rq->min_vruntime, (u64)(-(1LL << 20)));
#ifdef CONFIG_SMP
raw_spin_lock_init(&cfs_rq->removed.lock);
#endif
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 762be73972bd..e2cf6e48b165 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -513,6 +513,45 @@ struct cfs_bandwidth { };
#endif /* CONFIG_CGROUP_SCHED */
+/*
+ * u64_u32_load/u64_u32_store
+ *
+ * Use a copy of a u64 value to protect against data race. This is only
+ * applicable for 32-bits architectures.
+ */
+#ifdef CONFIG_64BIT
+# define u64_u32_load_copy(var, copy) var
+# define u64_u32_store_copy(var, copy, val) (var = val)
+#else
+# define u64_u32_load_copy(var, copy) \
+({ \
+ u64 __val, __val_copy; \
+ do { \
+ __val_copy = copy; \
+ /* \
+ * paired with u64_u32_store, ordering access \
+ * to var and copy. \
+ */ \
+ smp_rmb(); \
+ __val = var; \
+ } while (__val != __val_copy); \
+ __val; \
+})
+# define u64_u32_store_copy(var, copy, val) \
+do { \
+ typeof(val) __val = (val); \
+ var = __val; \
+ /* \
+ * paired with u64_u32_load, ordering access to var and \
+ * copy. \
+ */ \
+ smp_wmb(); \
+ copy = __val; \
+} while (0)
+#endif
+# define u64_u32_load(var) u64_u32_load_copy(var, var##_copy)
+# define u64_u32_store(var, val) u64_u32_store_copy(var, var##_copy, val)
+
/* CFS-related fields in a runqueue */
struct cfs_rq {
struct load_weight load;
@@ -553,7 +592,7 @@ struct cfs_rq {
*/
struct sched_avg avg;
#ifndef CONFIG_64BIT
- u64 load_last_update_time_copy;
+ u64 last_update_time_copy;
#endif
struct {
raw_spinlock_t lock ____cacheline_aligned;
--
2.25.1
From: Dietmar Eggemann <[email protected]>
Decouple the name of the per-cpu cpumask select_idle_mask from its usage
in select_idle_[cpu/capacity]() of the CFS run-queue selection
(select_task_rq_fair()).
This is to support the reuse of this cpumask in the Energy Aware
Scheduling (EAS) path (find_energy_efficient_cpu()) of the CFS run-queue
selection.
Signed-off-by: Dietmar Eggemann <[email protected]>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a62d25ec5b0d..f3f5540bae9e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9456,7 +9456,7 @@ static struct kmem_cache *task_group_cache __read_mostly;
#endif
DECLARE_PER_CPU(cpumask_var_t, load_balance_mask);
-DECLARE_PER_CPU(cpumask_var_t, select_idle_mask);
+DECLARE_PER_CPU(cpumask_var_t, select_rq_mask);
void __init sched_init(void)
{
@@ -9505,7 +9505,7 @@ void __init sched_init(void)
for_each_possible_cpu(i) {
per_cpu(load_balance_mask, i) = (cpumask_var_t)kzalloc_node(
cpumask_size(), GFP_KERNEL, cpu_to_node(i));
- per_cpu(select_idle_mask, i) = (cpumask_var_t)kzalloc_node(
+ per_cpu(select_rq_mask, i) = (cpumask_var_t)kzalloc_node(
cpumask_size(), GFP_KERNEL, cpu_to_node(i));
}
#endif /* CONFIG_CPUMASK_OFFSTACK */
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7cd1fb073fcf..f1e78f6adc98 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5848,7 +5848,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
/* Working cpumask for: load_balance, load_balance_newidle. */
DEFINE_PER_CPU(cpumask_var_t, load_balance_mask);
-DEFINE_PER_CPU(cpumask_var_t, select_idle_mask);
+DEFINE_PER_CPU(cpumask_var_t, select_rq_mask);
#ifdef CONFIG_NO_HZ_COMMON
@@ -6338,7 +6338,7 @@ static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd
*/
static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool has_idle_core, int target)
{
- struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
+ struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_rq_mask);
int i, cpu, idle_cpu = -1, nr = INT_MAX;
struct rq *this_rq = this_rq();
int this = smp_processor_id();
@@ -6424,7 +6424,7 @@ select_idle_capacity(struct task_struct *p, struct sched_domain *sd, int target)
int cpu, best_cpu = -1;
struct cpumask *cpus;
- cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
+ cpus = this_cpu_cpumask_var_ptr(select_rq_mask);
cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
task_util = uclamp_task_util(p);
--
2.25.1
The energy estimation in find_energy_efficient_cpu() (feec()) relies on
the computation of the effective utilization for each CPU of a perf domain
(PD). This effective utilization is then used as an estimation of the busy
time for this pd. The function effective_cpu_util() which gives this value,
scales the utilization relative to IRQ pressure on the CPU to take into
account that the IRQ time is hidden from the task clock. The IRQ scaling is
as follow:
effective_cpu_util = irq + (cpu_cap - irq)/cpu_cap * util
Where util is the sum of CFS/RT/DL utilization, cpu_cap the capacity of
the CPU and irq the IRQ avg time.
If now we take as an example a task placement which doesn't raise the OPP
on the candidate CPU, we can write the energy delta as:
delta = OPPcost/cpu_cap * (effective_cpu_util(cpu_util + task_util) -
effective_cpu_util(cpu_util))
= OPPcost/cpu_cap * (cpu_cap - irq)/cpu_cap * task_util
We end-up with an energy delta depending on the IRQ avg time, which is a
problem: first the time spent on IRQs by a CPU has no effect on the
additional energy that would be consumed by a task. Second, we don't want
to favour a CPU with a higher IRQ avg time value.
Nonetheless, we need to take the IRQ avg time into account. If a task
placement raises the PD's frequency, it will increase the energy cost for
the entire time where the CPU is busy. A solution is to only use
effective_cpu_util() with the CPU contribution part. The task contribution
is added separately and scaled according to prev_cpu's IRQ time.
No change for the FREQUENCY_UTIL component of the energy estimation. We
still want to get the actual frequency that would be selected after the
task placement.
Signed-off-by: Vincent Donnefort <[email protected]>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 97eb8afb336c..d17ef80487e4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6687,61 +6687,97 @@ static unsigned long cpu_util_next(int cpu, struct task_struct *p, int dst_cpu)
}
/*
- * compute_energy(): Estimates the energy that @pd would consume if @p was
- * migrated to @dst_cpu. compute_energy() predicts what will be the utilization
- * landscape of @pd's CPUs after the task migration, and uses the Energy Model
- * to compute what would be the energy if we decided to actually migrate that
- * task.
+ * energy_env - Utilization landscape for energy estimation.
+ * @task_busy_time: Utilization contribution by the task for which we test the
+ * placement. Given by eenv_task_busy_time().
+ * @pd_busy_time: Utilization of the whole perf domain without the task
+ * contribution. Given by eenv_pd_busy_time().
+ * @cpu_cap: Maximum CPU capacity for the perf domain.
+ * @pd_cap: Entire perf domain capacity. (pd->nr_cpus * cpu_cap).
+ */
+struct energy_env {
+ unsigned long task_busy_time;
+ unsigned long pd_busy_time;
+ unsigned long cpu_cap;
+ unsigned long pd_cap;
+};
+
+/*
+ * Compute the task busy time for compute_energy(). This time cannot be
+ * injected directly into effective_cpu_util() because of the IRQ scaling.
+ * The latter only makes sense with the most recent CPUs where the task has
+ * run.
*/
-static long
-compute_energy(struct task_struct *p, int dst_cpu, struct cpumask *cpus,
- struct perf_domain *pd)
+static inline void eenv_task_busy_time(struct energy_env *eenv,
+ struct task_struct *p, int prev_cpu)
{
- unsigned long max_util = 0, sum_util = 0, cpu_cap;
+ unsigned long max_cap = arch_scale_cpu_capacity(prev_cpu);
+ unsigned long irq = cpu_util_irq(cpu_rq(prev_cpu));
+
+ if (unlikely(irq >= max_cap)) {
+ eenv->task_busy_time = max_cap;
+ return;
+ }
+
+ eenv->task_busy_time =
+ scale_irq_capacity(task_util_est(p), irq, max_cap);
+}
+
+/*
+ * Compute the perf_domain (PD) busy time for compute_energy(). Based on the
+ * utilization for each @pd_cpus, it however doesn't take into account
+ * clamping since the ratio (utilization / cpu_capacity) is already enough to
+ * scale the EM reported power consumption at the (eventually clamped)
+ * cpu_capacity.
+ *
+ * The contribution of the task @p for which we want to estimate the
+ * energy cost is removed (by cpu_util_next()) and must be calculated
+ * separately (see eenv_task_busy_time). This ensures:
+ *
+ * - A stable PD utilization, no matter which CPU of that PD we want to place
+ * the task on.
+ *
+ * - A fair comparison between CPUs as the task contribution (task_util())
+ * will always be the same no matter which CPU utilization we rely on
+ * (util_avg or util_est).
+ *
+ * Set @eenv busy time for the PD that spans @pd_cpus. This busy time can't
+ * exceed @eenv->pd_cap.
+ */
+static inline void eenv_pd_busy_time(struct energy_env *eenv,
+ struct cpumask *pd_cpus,
+ struct task_struct *p)
+{
+ unsigned long busy_time = 0;
int cpu;
- cpu_cap = arch_scale_cpu_capacity(cpumask_first(cpus));
- cpu_cap -= arch_scale_thermal_pressure(cpumask_first(cpus));
+ for_each_cpu(cpu, pd_cpus) {
+ unsigned long util = cpu_util_next(cpu, p, -1);
- /*
- * The capacity state of CPUs of the current rd can be driven by CPUs
- * of another rd if they belong to the same pd. So, account for the
- * utilization of these CPUs too by masking pd with cpu_online_mask
- * instead of the rd span.
- *
- * If an entire pd is outside of the current rd, it will not appear in
- * its pd list and will not be accounted by compute_energy().
- */
- for_each_cpu(cpu, cpus) {
- unsigned long util_freq = cpu_util_next(cpu, p, dst_cpu);
- unsigned long cpu_util, util_running = util_freq;
- struct task_struct *tsk = NULL;
+ busy_time += effective_cpu_util(cpu, util, ENERGY_UTIL, NULL);
+ }
- /*
- * When @p is placed on @cpu:
- *
- * util_running = max(cpu_util, cpu_util_est) +
- * max(task_util, _task_util_est)
- *
- * while cpu_util_next is: max(cpu_util + task_util,
- * cpu_util_est + _task_util_est)
- */
- if (cpu == dst_cpu) {
- tsk = p;
- util_running =
- cpu_util_next(cpu, p, -1) + task_util_est(p);
- }
+ eenv->pd_busy_time = min(eenv->pd_cap, busy_time);
+}
- /*
- * Busy time computation: utilization clamping is not
- * required since the ratio (sum_util / cpu_capacity)
- * is already enough to scale the EM reported power
- * consumption at the (eventually clamped) cpu_capacity.
- */
- cpu_util = effective_cpu_util(cpu, util_running, ENERGY_UTIL,
- NULL);
+/*
+ * Compute the maximum utilization for compute_energy() when the task @p
+ * is placed on the cpu @dst_cpu.
+ *
+ * Returns the maximum utilization among @eenv->cpus. This utilization can't
+ * exceed @eenv->cpu_cap.
+ */
+static inline unsigned long
+eenv_pd_max_util(struct energy_env *eenv, struct cpumask *pd_cpus,
+ struct task_struct *p, int dst_cpu)
+{
+ unsigned long max_util = 0;
+ int cpu;
- sum_util += min(cpu_util, cpu_cap);
+ for_each_cpu(cpu, pd_cpus) {
+ struct task_struct *tsk = (cpu == dst_cpu) ? p : NULL;
+ unsigned long util = cpu_util_next(cpu, p, dst_cpu);
+ unsigned long cpu_util;
/*
* Performance domain frequency: utilization clamping
@@ -6750,12 +6786,30 @@ compute_energy(struct task_struct *p, int dst_cpu, struct cpumask *cpus,
* NOTE: in case RT tasks are running, by default the
* FREQUENCY_UTIL's utilization can be max OPP.
*/
- cpu_util = effective_cpu_util(cpu, util_freq, FREQUENCY_UTIL,
- tsk);
- max_util = max(max_util, min(cpu_util, cpu_cap));
+ cpu_util = effective_cpu_util(cpu, util, FREQUENCY_UTIL, tsk);
+ max_util = max(max_util, cpu_util);
}
- return em_cpu_energy(pd->em_pd, max_util, sum_util, cpu_cap);
+ return min(max_util, eenv->cpu_cap);
+}
+
+/*
+ * compute_energy(): Use the Energy Model to estimate the energy that @pd would
+ * consume for a given utilization landscape @eenv. If @dst_cpu < 0 the task
+ * contribution is removed from the energy estimation.
+ */
+static inline unsigned long
+compute_energy(struct energy_env *eenv, struct perf_domain *pd,
+ struct cpumask *pd_cpus, struct task_struct *p, int dst_cpu)
+{
+ unsigned long max_util = eenv_pd_max_util(eenv, pd_cpus, p, dst_cpu);
+ unsigned long busy_time = eenv->pd_busy_time;
+
+ if (dst_cpu >= 0)
+ busy_time = min(eenv->pd_cap,
+ eenv->pd_busy_time + eenv->task_busy_time);
+
+ return em_cpu_energy(pd->em_pd, max_util, busy_time, eenv->cpu_cap);
}
/*
@@ -6801,11 +6855,12 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
{
struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_rq_mask);
unsigned long prev_delta = ULONG_MAX, best_delta = ULONG_MAX;
- struct root_domain *rd = cpu_rq(smp_processor_id())->rd;
int cpu, best_energy_cpu = prev_cpu, target = -1;
- unsigned long cpu_cap, util, base_energy = 0;
+ struct root_domain *rd = this_rq()->rd;
+ unsigned long base_energy = 0;
struct sched_domain *sd;
struct perf_domain *pd;
+ struct energy_env eenv;
rcu_read_lock();
pd = rcu_dereference(rd->pd);
@@ -6828,22 +6883,36 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
if (!task_util_est(p))
goto unlock;
+ eenv_task_busy_time(&eenv, p, prev_cpu);
+
for (; pd; pd = pd->next) {
- unsigned long cur_delta, spare_cap, max_spare_cap = 0;
+ unsigned long cpu_cap, cpu_thermal_cap, util;
+ unsigned long cur_delta, max_spare_cap = 0;
bool compute_prev_delta = false;
unsigned long base_energy_pd;
int max_spare_cap_cpu = -1;
cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);
- for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
+ /* Account thermal pressure for the energy estimation */
+ cpu = cpumask_first(cpus);
+ cpu_thermal_cap = arch_scale_cpu_capacity(cpu);
+ cpu_thermal_cap -= arch_scale_thermal_pressure(cpu);
+
+ eenv.cpu_cap = cpu_thermal_cap;
+ eenv.pd_cap = 0;
+
+ for_each_cpu(cpu, cpus) {
+ eenv.pd_cap += cpu_thermal_cap;
+
+ if (!cpumask_test_cpu(cpu, sched_domain_span(sd)))
+ continue;
+
if (!cpumask_test_cpu(cpu, p->cpus_ptr))
continue;
util = cpu_util_next(cpu, p, cpu);
cpu_cap = capacity_of(cpu);
- spare_cap = cpu_cap;
- lsub_positive(&spare_cap, util);
/*
* Skip CPUs that cannot satisfy the capacity request.
@@ -6856,15 +6925,17 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
if (!fits_capacity(util, cpu_cap))
continue;
+ lsub_positive(&cpu_cap, util);
+
if (cpu == prev_cpu) {
/* Always use prev_cpu as a candidate. */
compute_prev_delta = true;
- } else if (spare_cap > max_spare_cap) {
+ } else if (cpu_cap > max_spare_cap) {
/*
* Find the CPU with the maximum spare capacity
* in the performance domain.
*/
- max_spare_cap = spare_cap;
+ max_spare_cap = cpu_cap;
max_spare_cap_cpu = cpu;
}
}
@@ -6873,12 +6944,14 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
continue;
/* Compute the 'base' energy of the pd, without @p */
- base_energy_pd = compute_energy(p, -1, cpus, pd);
+ eenv_pd_busy_time(&eenv, cpus, p);
+ base_energy_pd = compute_energy(&eenv, pd, cpus, p, -1);
base_energy += base_energy_pd;
/* Evaluate the energy impact of using prev_cpu. */
if (compute_prev_delta) {
- prev_delta = compute_energy(p, prev_cpu, cpus, pd);
+ prev_delta = compute_energy(&eenv, pd, cpus, p,
+ prev_cpu);
if (prev_delta < base_energy_pd)
goto unlock;
prev_delta -= base_energy_pd;
@@ -6887,8 +6960,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
/* Evaluate the energy impact of using max_spare_cap_cpu. */
if (max_spare_cap_cpu >= 0) {
- cur_delta = compute_energy(p, max_spare_cap_cpu, cpus,
- pd);
+ cur_delta = compute_energy(&eenv, pd, cpus, p,
+ max_spare_cap_cpu);
if (cur_delta < base_energy_pd)
goto unlock;
cur_delta -= base_energy_pd;
--
2.25.1
From: Dietmar Eggemann <[email protected]>
effective_cpu_util() already has a `int cpu' parameter which allows to
retrieve the CPU capacity scale factor (or maximum CPU capacity) inside
this function via an arch_scale_cpu_capacity(cpu).
A lot of code calling effective_cpu_util() (or the shim
sched_cpu_util()) needs the maximum CPU capacity, i.e. it will call
arch_scale_cpu_capacity() already.
But not having to pass it into effective_cpu_util() will make the EAS
wake-up code easier, especially when the maximum CPU capacity reduced
by the thermal pressure is passed through the EAS wake-up functions.
Due to the asymmetric CPU capacity support of arm/arm64 architectures,
arch_scale_cpu_capacity(int cpu) is a per-CPU variable read access via
per_cpu(cpu_scale, cpu) on such a system.
On all other architectures it is a a compile-time constant
(SCHED_CAPACITY_SCALE).
Signed-off-by: Dietmar Eggemann <[email protected]>
diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c
index bca2f912d349..024dba4e6575 100644
--- a/drivers/powercap/dtpm_cpu.c
+++ b/drivers/powercap/dtpm_cpu.c
@@ -71,34 +71,19 @@ static u64 set_pd_power_limit(struct dtpm *dtpm, u64 power_limit)
static u64 scale_pd_power_uw(struct cpumask *pd_mask, u64 power)
{
- unsigned long max = 0, sum_util = 0;
+ unsigned long max, sum_util = 0;
int cpu;
- for_each_cpu_and(cpu, pd_mask, cpu_online_mask) {
-
- /*
- * The capacity is the same for all CPUs belonging to
- * the same perf domain, so a single call to
- * arch_scale_cpu_capacity() is enough. However, we
- * need the CPU parameter to be initialized by the
- * loop, so the call ends up in this block.
- *
- * We can initialize 'max' with a cpumask_first() call
- * before the loop but the bits computation is not
- * worth given the arch_scale_cpu_capacity() just
- * returns a value where the resulting assembly code
- * will be optimized by the compiler.
- */
- max = arch_scale_cpu_capacity(cpu);
- sum_util += sched_cpu_util(cpu, max);
- }
-
/*
- * In the improbable case where all the CPUs of the perf
- * domain are offline, 'max' will be zero and will lead to an
- * illegal operation with a zero division.
+ * The capacity is the same for all CPUs belonging to
+ * the same perf domain.
*/
- return max ? (power * ((sum_util << 10) / max)) >> 10 : 0;
+ max = arch_scale_cpu_capacity(cpumask_first(pd_mask));
+
+ for_each_cpu_and(cpu, pd_mask, cpu_online_mask)
+ sum_util += sched_cpu_util(cpu);
+
+ return (power * ((sum_util << 10) / max)) >> 10;
}
static u64 get_pd_power_uw(struct dtpm *dtpm)
diff --git a/drivers/thermal/cpufreq_cooling.c b/drivers/thermal/cpufreq_cooling.c
index 0bfb8eebd126..3f514ff3d9aa 100644
--- a/drivers/thermal/cpufreq_cooling.c
+++ b/drivers/thermal/cpufreq_cooling.c
@@ -137,11 +137,9 @@ static u32 cpu_power_to_freq(struct cpufreq_cooling_device *cpufreq_cdev,
static u32 get_load(struct cpufreq_cooling_device *cpufreq_cdev, int cpu,
int cpu_idx)
{
- unsigned long max = arch_scale_cpu_capacity(cpu);
- unsigned long util;
+ unsigned long util = sched_cpu_util(cpu);
- util = sched_cpu_util(cpu, max);
- return (util * 100) / max;
+ return (util * 100) / arch_scale_cpu_capacity(cpu);
}
#else /* !CONFIG_SMP */
static u32 get_load(struct cpufreq_cooling_device *cpufreq_cdev, int cpu,
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 67f06f72c50e..c1705effb3a4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2255,7 +2255,7 @@ static inline bool owner_on_cpu(struct task_struct *owner)
}
/* Returns effective CPU energy utilization, as seen by the scheduler */
-unsigned long sched_cpu_util(int cpu, unsigned long max);
+unsigned long sched_cpu_util(int cpu);
#endif /* CONFIG_SMP */
#ifdef CONFIG_RSEQ
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 068c088e9584..a62d25ec5b0d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7061,12 +7061,14 @@ struct task_struct *idle_task(int cpu)
* required to meet deadlines.
*/
unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
- unsigned long max, enum cpu_util_type type,
+ enum cpu_util_type type,
struct task_struct *p)
{
- unsigned long dl_util, util, irq;
+ unsigned long dl_util, util, irq, max;
struct rq *rq = cpu_rq(cpu);
+ max = arch_scale_cpu_capacity(cpu);
+
if (!uclamp_is_used() &&
type == FREQUENCY_UTIL && rt_rq_is_runnable(&rq->rt)) {
return max;
@@ -7146,10 +7148,9 @@ unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
return min(max, util);
}
-unsigned long sched_cpu_util(int cpu, unsigned long max)
+unsigned long sched_cpu_util(int cpu)
{
- return effective_cpu_util(cpu, cpu_util_cfs(cpu), max,
- ENERGY_UTIL, NULL);
+ return effective_cpu_util(cpu, cpu_util_cfs(cpu), ENERGY_UTIL, NULL);
}
#endif /* CONFIG_SMP */
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 3dbf351d12d5..1207c78f85c1 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -157,11 +157,10 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
static void sugov_get_util(struct sugov_cpu *sg_cpu)
{
struct rq *rq = cpu_rq(sg_cpu->cpu);
- unsigned long max = arch_scale_cpu_capacity(sg_cpu->cpu);
- sg_cpu->max = max;
+ sg_cpu->max = arch_scale_cpu_capacity(sg_cpu->cpu);
sg_cpu->bw_dl = cpu_bw_dl(rq);
- sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu), max,
+ sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu),
FREQUENCY_UTIL, NULL);
}
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e234d015657f..7cd1fb073fcf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6697,12 +6697,11 @@ static long
compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
{
struct cpumask *pd_mask = perf_domain_span(pd);
- unsigned long cpu_cap = arch_scale_cpu_capacity(cpumask_first(pd_mask));
- unsigned long max_util = 0, sum_util = 0;
- unsigned long _cpu_cap = cpu_cap;
+ unsigned long max_util = 0, sum_util = 0, cpu_cap;
int cpu;
- _cpu_cap -= arch_scale_thermal_pressure(cpumask_first(pd_mask));
+ cpu_cap = arch_scale_cpu_capacity(cpumask_first(pd_mask));
+ cpu_cap -= arch_scale_thermal_pressure(cpumask_first(pd_mask));
/*
* The capacity state of CPUs of the current rd can be driven by CPUs
@@ -6739,10 +6738,10 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
* is already enough to scale the EM reported power
* consumption at the (eventually clamped) cpu_capacity.
*/
- cpu_util = effective_cpu_util(cpu, util_running, cpu_cap,
- ENERGY_UTIL, NULL);
+ cpu_util = effective_cpu_util(cpu, util_running, ENERGY_UTIL,
+ NULL);
- sum_util += min(cpu_util, _cpu_cap);
+ sum_util += min(cpu_util, cpu_cap);
/*
* Performance domain frequency: utilization clamping
@@ -6751,12 +6750,12 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
* NOTE: in case RT tasks are running, by default the
* FREQUENCY_UTIL's utilization can be max OPP.
*/
- cpu_util = effective_cpu_util(cpu, util_freq, cpu_cap,
- FREQUENCY_UTIL, tsk);
- max_util = max(max_util, min(cpu_util, _cpu_cap));
+ cpu_util = effective_cpu_util(cpu, util_freq, FREQUENCY_UTIL,
+ tsk);
+ max_util = max(max_util, min(cpu_util, cpu_cap));
}
- return em_cpu_energy(pd->em_pd, max_util, sum_util, _cpu_cap);
+ return em_cpu_energy(pd->em_pd, max_util, sum_util, cpu_cap);
}
/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 2f6446295e7d..0b2eebbaa0d3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2874,7 +2874,7 @@ enum cpu_util_type {
};
unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
- unsigned long max, enum cpu_util_type type,
+ enum cpu_util_type type,
struct task_struct *p);
static inline unsigned long cpu_bw_dl(struct rq *rq)
--
2.25.1
On 12/04/2022 15:42, Vincent Donnefort wrote:
Nitpick: s/v3/v4 in cover letter
> find_energy_efficient() (feec()) will migrate a task to save energy only
s/find_energy_efficient/find_energy_efficient_cpu
[...]
LGTM. For the whole patch-set:
Reviewed-by: Dietmar Eggemann <[email protected]>
On Tue, Apr 12, 2022 at 02:42:14PM +0100,
Vincent Donnefort wrote:
> Introducing macro helpers u64_u32_{store,load}() to factorize lockless
> accesses to u64 variables for 32-bits architectures.
>
> Users are for now cfs_rq.min_vruntime and sched_avg.last_update_time. To
> accommodate the later where the copy lies outside of the structure
> (cfs_rq.last_udpate_time_copy instead of sched_avg.last_update_time_copy),
> use the _copy() version of those helpers.
>
> Those new helpers encapsulate smp_rmb() and smp_wmb() synchronization and
> therefore, have a small penalty in set_task_rq_fair() and init_cfs_rq().
>
> Signed-off-by: Vincent Donnefort <[email protected]>
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 3eba0dcc4962..5dd38c9df0cc 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -600,11 +600,8 @@ static void update_min_vruntime(struct cfs_rq *cfs_rq)
> }
>
> /* ensure we never gain time by being placed backwards. */
> - cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime);
> -#ifndef CONFIG_64BIT
> - smp_wmb();
> - cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
> -#endif
> + u64_u32_store(cfs_rq->min_vruntime,
> + max_vruntime(cfs_rq->min_vruntime, vruntime));
> }
>
> static inline bool __entity_less(struct rb_node *a, const struct rb_node *b)
> @@ -3301,6 +3298,11 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
> }
>
> #ifdef CONFIG_SMP
> +static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
> +{
> + return u64_u32_load_copy(cfs_rq->avg.last_update_time,
> + cfs_rq->last_update_time_copy);
> +}
> #ifdef CONFIG_FAIR_GROUP_SCHED
> /*
> * Because list_add_leaf_cfs_rq always places a child cfs_rq on the list
> @@ -3411,27 +3413,9 @@ void set_task_rq_fair(struct sched_entity *se,
> if (!(se->avg.last_update_time && prev))
> return;
>
> -#ifndef CONFIG_64BIT
> - {
> - u64 p_last_update_time_copy;
> - u64 n_last_update_time_copy;
> -
> - do {
> - p_last_update_time_copy = prev->load_last_update_time_copy;
> - n_last_update_time_copy = next->load_last_update_time_copy;
> -
> - smp_rmb();
> + p_last_update_time = cfs_rq_last_update_time(prev);
> + n_last_update_time = cfs_rq_last_update_time(next);
Seperate the load of prev cfs rq and next cfs rq seems not wrong to me.
> - p_last_update_time = prev->avg.last_update_time;
> - n_last_update_time = next->avg.last_update_time;
> -
> - } while (p_last_update_time != p_last_update_time_copy ||
> - n_last_update_time != n_last_update_time_copy);
> - }
> -#else
> - p_last_update_time = prev->avg.last_update_time;
> - n_last_update_time = next->avg.last_update_time;
> -#endif
> __update_load_avg_blocked_se(p_last_update_time, se);
> se->avg.last_update_time = n_last_update_time;
> }
> @@ -3786,8 +3770,9 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
> decayed |= __update_load_avg_cfs_rq(now, cfs_rq);
>
> #ifndef CONFIG_64BIT
> - smp_wmb();
> - cfs_rq->load_last_update_time_copy = sa->last_update_time;
> + u64_u32_store_copy(sa->last_update_time,
> + cfs_rq->last_update_time_copy,
> + sa->last_update_time);
> #endif
>
> return decayed;
> @@ -3921,27 +3906,6 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> }
> }
>
> -#ifndef CONFIG_64BIT
> -static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
> -{
> - u64 last_update_time_copy;
> - u64 last_update_time;
> -
> - do {
> - last_update_time_copy = cfs_rq->load_last_update_time_copy;
> - smp_rmb();
> - last_update_time = cfs_rq->avg.last_update_time;
> - } while (last_update_time != last_update_time_copy);
> -
> - return last_update_time;
> -}
> -#else
> -static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
> -{
> - return cfs_rq->avg.last_update_time;
> -}
> -#endif
> -
> /*
> * Synchronize entity load avg of dequeued entity without locking
> * the previous rq.
> @@ -6991,21 +6955,8 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu)
> if (READ_ONCE(p->__state) == TASK_WAKING) {
> struct sched_entity *se = &p->se;
> struct cfs_rq *cfs_rq = cfs_rq_of(se);
> - u64 min_vruntime;
>
> -#ifndef CONFIG_64BIT
> - u64 min_vruntime_copy;
> -
> - do {
> - min_vruntime_copy = cfs_rq->min_vruntime_copy;
> - smp_rmb();
> - min_vruntime = cfs_rq->min_vruntime;
> - } while (min_vruntime != min_vruntime_copy);
> -#else
> - min_vruntime = cfs_rq->min_vruntime;
> -#endif
> -
> - se->vruntime -= min_vruntime;
> + se->vruntime -= u64_u32_load(cfs_rq->min_vruntime);
> }
>
> if (p->on_rq == TASK_ON_RQ_MIGRATING) {
> @@ -11453,10 +11404,7 @@ static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
> void init_cfs_rq(struct cfs_rq *cfs_rq)
> {
> cfs_rq->tasks_timeline = RB_ROOT_CACHED;
> - cfs_rq->min_vruntime = (u64)(-(1LL << 20));
> -#ifndef CONFIG_64BIT
> - cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
> -#endif
> + u64_u32_store(cfs_rq->min_vruntime, (u64)(-(1LL << 20)));
> #ifdef CONFIG_SMP
> raw_spin_lock_init(&cfs_rq->removed.lock);
> #endif
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 762be73972bd..e2cf6e48b165 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -513,6 +513,45 @@ struct cfs_bandwidth { };
>
> #endif /* CONFIG_CGROUP_SCHED */
>
> +/*
> + * u64_u32_load/u64_u32_store
> + *
> + * Use a copy of a u64 value to protect against data race. This is only
> + * applicable for 32-bits architectures.
> + */
> +#ifdef CONFIG_64BIT
> +# define u64_u32_load_copy(var, copy) var
> +# define u64_u32_store_copy(var, copy, val) (var = val)
> +#else
> +# define u64_u32_load_copy(var, copy) \
> +({ \
> + u64 __val, __val_copy; \
> + do { \
> + __val_copy = copy; \
> + /* \
> + * paired with u64_u32_store, ordering access \
> + * to var and copy. \
> + */ \
> + smp_rmb(); \
> + __val = var; \
> + } while (__val != __val_copy); \
> + __val; \
> +})
> +# define u64_u32_store_copy(var, copy, val) \
> +do { \
> + typeof(val) __val = (val); \
> + var = __val; \
> + /* \
> + * paired with u64_u32_load, ordering access to var and \
> + * copy. \
> + */ \
> + smp_wmb(); \
> + copy = __val; \
`copy = __val;` should be `copy = var`.
If var equal to val we do not need to do store. Check this condition
in the above macro to avoid a redundant store.
if (var != __val)
var = __val;
Catching up a little and droping a little..
Thanks,
Tao
> +} while (0)
> +#endif
> +# define u64_u32_load(var) u64_u32_load_copy(var, var##_copy)
> +# define u64_u32_store(var, val) u64_u32_store_copy(var, var##_copy, val)
> +
> /* CFS-related fields in a runqueue */
> struct cfs_rq {
> struct load_weight load;
> @@ -553,7 +592,7 @@ struct cfs_rq {
> */
> struct sched_avg avg;
> #ifndef CONFIG_64BIT
> - u64 load_last_update_time_copy;
> + u64 last_update_time_copy;
> #endif
> struct {
> raw_spinlock_t lock ____cacheline_aligned;
> --
> 2.25.1
>
[...]
>> +#ifdef CONFIG_64BIT
>> +# define u64_u32_load_copy(var, copy) var
>> +# define u64_u32_store_copy(var, copy, val) (var = val)
>> +#else
>> +# define u64_u32_load_copy(var, copy) \
>> +({ \
>> + u64 __val, __val_copy; \
>> + do { \
>> + __val_copy = copy; \
>> + /* \
>> + * paired with u64_u32_store, ordering access \
>> + * to var and copy. \
>> + */ \
>> + smp_rmb(); \
>> + __val = var; \
>> + } while (__val != __val_copy); \
>> + __val; \
>> +})
>> +# define u64_u32_store_copy(var, copy, val) \
>> +do { \
>> + typeof(val) __val = (val); \
>> + var = __val; \
>> + /* \
>> + * paired with u64_u32_load, ordering access to var and \
>> + * copy. \
>> + */ \
>> + smp_wmb(); \
>> + copy = __val; \
>
> `copy = __val;` should be `copy = var`.
>
> If var equal to val we do not need to do store. Check this condition
> in the above macro to avoid a redundant store.
>
> if (var != __val)
> var = __val;
Judging by the users of this macro, var = val is very much unlikely to
happen. Also, I don't think we want to waste a if here.
[...]