Changes in v5:
- Collected tags in commit messages.
- Link to v4: https://lore.kernel.org/lkml/[email protected]/
Changes in v4:
- Updated commit messages: set Fixes tag to a proper commit,
comment about SDM macro in a debug commit.
- Link to v3: https://lore.kernel.org/lkml/[email protected]/
Changes in v3:
- Remove levels table change from the documentation patch
- Link to v2: https://lore.kernel.org/lkml/[email protected]/
Changes in v2:
- Split debug.c change in a separate commit and move new "level"
after "groups_flags"
- Added "Fixes" tag and updated commit message
- Update domain levels cgroup-v1/cpusets.rst documentation
- Link to v1: https://lore.kernel.org/all/[email protected]/
During the upgrade from Linux 5.4 we found a small (around 3%)
performance regression which was tracked to commit
c5b0a7eefc70150caf23e37bc9d639c68c87a097
sched/fair: Remove sysctl_sched_migration_cost condition
With a default value of 500us, sysctl_sched_migration_cost is
significanlty higher than the cost of load_balance. Remove the
condition and rely on the sd->max_newidle_lb_cost to abort
newidle_balance.
Looks like "newidle" balancing is beneficial for a lot of workloads,
just not for this specific one. The workload is video encoding, there
are 100s-1000s of threads, some are synchronized with mutexes and
conditional variables. The process aims to have a portion of CPU idle,
so no CPU cores are 100% busy. Perhaps, the performance impact we see
comes from additional processing in the scheduler and additional cost
like more cache misses, and not from an incorrect balancing. See
perf output below.
My understanding is that "sched_relax_domain_level" cgroup parameter
should control if sched_balance_newidle() is called and what's the scope
of the balancing is, but it doesn't fully work for this case.
cpusets.rst documentation:
> The 'cpuset.sched_relax_domain_level' file allows you to request changing
> this searching range as you like. This file takes int value which
> indicates size of searching range in levels ideally as follows,
> otherwise initial value -1 that indicates the cpuset has no request.
>
> ====== ===========================================================
> -1 no request. use system default or follow request of others.
> 0 no search.
> 1 search siblings (hyperthreads in a core).
> 2 search cores in a package.
> 3 search cpus in a node [= system wide on non-NUMA system]
> 4 search nodes in a chunk of node [on NUMA system]
> 5 search system wide [on NUMA system]
> ====== ===========================================================
Setting cpuset.sched_relax_domain_level to 0 works as 1.
On a dual-CPU server, domains and levels are as follows:
domain 0: level 0, SMT
domain 1: level 2, MC
domain 2: level 5, NUMA
So, to support "0 no search", the value in
cpuset.sched_relax_domain_level should disable SD_BALANCE_NEWIDLE for a
specified level and keep it enabled for prior levels. For example, SMT
level is 0, so sched_relax_domain_level=0 should exclude levels >=0.
Instead, cpuset.sched_relax_domain_level enables the specified level,
which effectively removes "no search" option. See below for domain
flags for all cpuset.sched_relax_domain_level values.
Proposed patch allows clearing SD_BALANCE_NEWIDLE flags when
cpuset.sched_relax_domain_level is set to 0 and extends max
value validation range beyond sched_domain_level_max. This allows
setting SD_BALANCE_NEWIDLE on all levels and override platform
default if it does not include all levels.
Thanks
=========================
Perf output for a simimar workload/test case shows that newidle_balance
(now renamed to sched_balance_newidle) is called when handling futex and
nanosleep syscalls:
8.74% 0.40% a.out [kernel.vmlinux] [k] entry_SYSCALL_64
8.34% entry_SYSCALL_64
- do_syscall_64
- 5.50% __x64_sys_futex
- 5.42% do_futex
- 3.79% futex_wait
- 3.74% __futex_wait
- 3.53% futex_wait_queue
- 3.45% schedule
- 3.43% __schedule
- 2.06% pick_next_task
- 1.93% pick_next_task_fair
- 1.87% newidle_balance
- 1.52% load_balance
- 1.16% find_busiest_group
- 1.13% update_sd_lb_stats.constprop.0
1.01% update_sg_lb_stats
- 0.83% dequeue_task_fair
0.66% dequeue_entity
- 1.57% futex_wake
- 1.22% wake_up_q
- 1.20% try_to_wake_up
0.58% select_task_rq_fair
- 2.44% __x64_sys_nanosleep
- 2.36% hrtimer_nanosleep
- 2.33% do_nanosleep
- 2.05% schedule
- 2.03% __schedule
- 1.23% pick_next_task
- 1.15% pick_next_task_fair
- 1.12% newidle_balance
- 0.90% load_balance
- 0.68% find_busiest_group
- 0.66% update_sd_lb_stats.constprop.0
0.59% update_sg_lb_stats
0.52% dequeue_task_fair
When newidle_balance is disabled (or when using older kernels), perf
output is:
6.37% 0.41% a.out [kernel.vmlinux] [k] entry_SYSCALL_64
5.96% entry_SYSCALL_64
- do_syscall_64
- 3.97% __x64_sys_futex
- 3.89% do_futex
- 2.32% futex_wait
- 2.27% __futex_wait
- 2.05% futex_wait_queue
- 1.98% schedule
- 1.96% __schedule
- 0.81% dequeue_task_fair
0.66% dequeue_entity
- 0.64% pick_next_task
0.51% pick_next_task_fair
- 1.52% futex_wake
- 1.15% wake_up_q
- try_to_wake_up
0.59% select_task_rq_fair
- 1.58% __x64_sys_nanosleep
- 1.52% hrtimer_nanosleep
- 1.48% do_nanosleep
- 1.20% schedule
- 1.19% __schedule
0.53% dequeue_task_fair
Without a patch:
=========================
CPUs: 2 Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz
# uname -r
6.8.1
# numactl -H
available: 2 nodes (0-1)
node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 24 25 26 27 28 29 30 31 32 33 34 35
node 0 size: 63962 MB
node 0 free: 59961 MB
node 1 cpus: 12 13 14 15 16 17 18 19 20 21 22 23 36 37 38 39 40 41 42 43 44 45 46 47
node 1 size: 64446 MB
node 1 free: 63338 MB
node distances:
node 0 1
0: 10 21
1: 21 10
# head /proc/schedstat
version 15
timestamp 4295347219
cpu0 0 0 0 0 0 0 3035466036 858375615 67578
domain0 0000,01000001 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0...
domain1 000f,ff000fff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0...
domain2 ffff,ffffffff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0...
# cd /sys/kernel/debug/sched/domains
# echo -1 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
# grep . cpu0/*/{name,flags,groups_flags,max_newidle_lb_cost}
cpu0/domain0/name:SMT
cpu0/domain1/name:MC
cpu0/domain2/name:NUMA
cpu0/domain0/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain1/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain2/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SERIALIZE SD_OVERLAP
SD_NUMA
cpu0/domain1/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC
SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_CPUCAPACITY SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain2/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC
SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain0/max_newidle_lb_cost:2236
cpu0/domain1/max_newidle_lb_cost:3444
cpu0/domain2/max_newidle_lb_cost:4590
# echo 0 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
# grep . cpu0/*/{flags,groups_flags,max_newidle_lb_cost}
cpu0/domain0/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain1/flags:SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain2/flags:SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SERIALIZE SD_OVERLAP SD_NUMA
cpu0/domain1/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC
SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_CPUCAPACITY SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain2/groups_flags:SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain0/max_newidle_lb_cost:0
cpu0/domain1/max_newidle_lb_cost:0
cpu0/domain2/max_newidle_lb_cost:0
# echo 1 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
# grep . cpu0/*/{flags,groups_flags,max_newidle_lb_cost}
cpu0/domain0/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain1/flags:SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain2/flags:SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SERIALIZE SD_OVERLAP SD_NUMA
cpu0/domain1/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC
SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_CPUCAPACITY SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain2/groups_flags:SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain0/max_newidle_lb_cost:309
cpu0/domain1/max_newidle_lb_cost:0
cpu0/domain2/max_newidle_lb_cost:0
# echo 2 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
# grep . cpu0/*/{flags,groups_flags,max_newidle_lb_cost}
cpu0/domain0/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain1/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain2/flags:SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SERIALIZE SD_OVERLAP SD_NUMA
cpu0/domain1/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC
SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_CPUCAPACITY SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain2/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC
SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain0/max_newidle_lb_cost:276
cpu0/domain1/max_newidle_lb_cost:2776
cpu0/domain2/max_newidle_lb_cost:0
# echo 3 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
# grep . cpu0/*/{flags,groups_flags,max_newidle_lb_cost}
cpu0/domain0/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain1/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain2/flags:SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SERIALIZE SD_OVERLAP SD_NUMA
cpu0/domain1/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC
SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_CPUCAPACITY SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain2/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC
SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain0/max_newidle_lb_cost:289
cpu0/domain1/max_newidle_lb_cost:3192
cpu0/domain2/max_newidle_lb_cost:0
# echo 4 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
# grep . cpu0/*/{flags,groups_flags,max_newidle_lb_cost}
cpu0/domain0/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain1/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK
SD_WAKE_AFFINE SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain2/flags:SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SERIALIZE SD_OVERLAP SD_NUMA
cpu0/domain1/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC
SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_CPUCAPACITY SD_SHARE_PKG_RESOURCES
SD_PREFER_SIBLING
cpu0/domain2/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC
SD_BALANCE_FORK SD_WAKE_AFFINE
SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING
cpu0/domain0/max_newidle_lb_cost:1306
cpu0/domain1/max_newidle_lb_cost:1999
cpu0/domain2/max_newidle_lb_cost:0
# echo 5 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
bash: echo: write error: Invalid argument
=========================
The same system with the patch applied:
=========================
# cd /sys/kernel/debug/sched/domains
# echo -1 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
# grep . cpu0/*/{name,level,flags,groups_flags}
cpu0/domain0/name:SMT
cpu0/domain1/name:MC
cpu0/domain2/name:NUMA
cpu0/domain0/level:0
cpu0/domain1/level:2
cpu0/domain2/level:5
cpu0/domain0/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain1/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain2/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain1/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain2/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
# echo 0 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
# grep . cpu0/*/{flags,groups_flags}
cpu0/domain0/flags:SD_BALANCE_EXEC ...
cpu0/domain1/flags:SD_BALANCE_EXEC ...
cpu0/domain2/flags:SD_BALANCE_EXEC ...
cpu0/domain1/groups_flags:SD_BALANCE_EXEC ...
cpu0/domain2/groups_flags:SD_BALANCE_EXEC ...
# echo 1 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
# grep . cpu0/*/{flags,groups_flags}
cpu0/domain0/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain1/flags:SD_BALANCE_EXEC ...
cpu0/domain2/flags:SD_BALANCE_EXEC ...
cpu0/domain1/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain2/groups_flags:SD_BALANCE_EXEC ...
[skip 2, same as 1]
# echo 3 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
# grep . cpu0/*/{flags,groups_flags}
cpu0/domain0/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain1/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain2/flags:SD_BALANCE_EXEC ...
cpu0/domain1/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain2/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
[skip 4 and 5, same as 3]
# echo 6 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
# grep . cpu0/*/{flags,groups_flags}
cpu0/domain0/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain1/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain2/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain1/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
cpu0/domain2/groups_flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC ...
# echo 7 > /sys/fs/cgroup/cpuset/cpuset.sched_relax_domain_level
bash: echo: write error: Invalid argument
=========================
Vitalii Bursov (3):
sched/fair: allow disabling sched_balance_newidle with
sched_relax_domain_level
sched/debug: dump domains' level
docs: cgroup-v1: clarify that domain levels are system-specific
Documentation/admin-guide/cgroup-v1/cpusets.rst | 7 ++++++-
kernel/cgroup/cpuset.c | 2 +-
kernel/sched/debug.c | 1 +
kernel/sched/topology.c | 2 +-
4 files changed, 9 insertions(+), 3 deletions(-)
--
2.20.1
Knowing domain's level exactly can be useful when setting
relax_domain_level or cpuset.sched_relax_domain_level
Usage:
cat /debug/sched/domains/cpu0/domain1/level
to dump cpu0 domain1's level.
SDM macro is not used because sd->level is int and
it would hide the type mismatch between int and u32.
Signed-off-by: Vitalii Bursov <[email protected]>
Acked-by: Vincent Guittot <[email protected]>
Tested-by: Dietmar Eggemann <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
---
kernel/sched/debug.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 8d5d98a5834d..c1eb9a1afd13 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -425,6 +425,7 @@ static void register_sd(struct sched_domain *sd, struct dentry *parent)
debugfs_create_file("flags", 0444, parent, &sd->flags, &sd_flags_fops);
debugfs_create_file("groups_flags", 0444, parent, &sd->groups->flags, &sd_flags_fops);
+ debugfs_create_u32("level", 0444, parent, (u32 *)&sd->level);
}
void update_sched_domain_debugfs(void)
--
2.20.1
Change relax_domain_level checks so that it would be possible
to include or exclude all domains from newidle balancing.
This matches the behavior described in the documentation:
-1 no request. use system default or follow request of others.
0 no search.
1 search siblings (hyperthreads in a core).
"2" enables levels 0 and 1, level_max excludes the last (level_max)
level, and level_max+1 includes all levels.
Fixes: 1d3504fcf560 ("sched, cpuset: customize sched domains, core")
Signed-off-by: Vitalii Bursov <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
Tested-by: Dietmar Eggemann <[email protected]>
---
kernel/cgroup/cpuset.c | 2 +-
kernel/sched/topology.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index a10e4bd0c0c1..c12b9fdb22a4 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2941,7 +2941,7 @@ bool current_cpuset_is_being_rebound(void)
static int update_relax_domain_level(struct cpuset *cs, s64 val)
{
#ifdef CONFIG_SMP
- if (val < -1 || val >= sched_domain_level_max)
+ if (val < -1 || val > sched_domain_level_max + 1)
return -EINVAL;
#endif
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 1d6eefa4032e..a6994a1fcc90 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1474,7 +1474,7 @@ static void set_domain_attribute(struct sched_domain *sd,
} else
request = attr->relax_domain_level;
- if (sd->level > request) {
+ if (sd->level >= request) {
/* Turn off idle balance on this domain: */
sd->flags &= ~(SD_BALANCE_WAKE|SD_BALANCE_NEWIDLE);
}
--
2.20.1