* [PATCH v2] sched/fair: Optimize select_idle_core
@ 2019-12-06 17:24 Srikar Dronamraju
2020-01-22 13:55 ` Mel Gorman
` (2 more replies)
0 siblings, 3 replies; 5+ messages in thread
From: Srikar Dronamraju @ 2019-12-06 17:24 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra
Cc: LKML, Mel Gorman, Rik van Riel, Srikar Dronamraju,
Thomas Gleixner, Valentin Schneider, Vincent Guittot
Currently we loop through all threads of a core to evaluate if the core is
idle or not. This is unnecessary. If a thread of a core is not idle, skip
evaluating other threads of a core. Also while clearing the cpumask, bits
of all CPUs of a core can be cleared in one-shot.
Collecting ticks on a Power 9 SMT 8 system around select_idle_core
while running schbench shows us
(units are in ticks, hence lesser is better)
Without patch
N Min Max Median Avg Stddev
x 130 151 1083 284 322.72308 144.41494
With patch
N Min Max Median Avg Stddev Improvement
x 164 88 610 201 225.79268 106.78943 30.03%
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
Changelog v1->v2:
Updated patch description with measurements made from a debug patch.
kernel/sched/fair.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 69a81a5709ff..b9d628128cfc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5872,10 +5872,12 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
bool idle = true;
for_each_cpu(cpu, cpu_smt_mask(core)) {
- __cpumask_clear_cpu(cpu, cpus);
- if (!available_idle_cpu(cpu))
+ if (!available_idle_cpu(cpu)) {
idle = false;
+ break;
+ }
}
+ cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
if (idle)
return core;
--
2.18.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2] sched/fair: Optimize select_idle_core
2019-12-06 17:24 [PATCH v2] sched/fair: Optimize select_idle_core Srikar Dronamraju
@ 2020-01-22 13:55 ` Mel Gorman
2020-01-22 14:22 ` Valentin Schneider
2020-01-24 13:32 ` Srikar Dronamraju
2020-01-29 11:32 ` [tip: sched/core] sched/fair: Optimize select_idle_core() tip-bot2 for Srikar Dronamraju
2 siblings, 1 reply; 5+ messages in thread
From: Mel Gorman @ 2020-01-22 13:55 UTC (permalink / raw)
To: Srikar Dronamraju
Cc: Ingo Molnar, Peter Zijlstra, LKML, Rik van Riel, Thomas Gleixner,
Valentin Schneider, Vincent Guittot
On Fri, Dec 06, 2019 at 10:54:22PM +0530, Srikar Dronamraju wrote:
> Currently we loop through all threads of a core to evaluate if the core is
> idle or not. This is unnecessary. If a thread of a core is not idle, skip
> evaluating other threads of a core. Also while clearing the cpumask, bits
> of all CPUs of a core can be cleared in one-shot.
>
> Collecting ticks on a Power 9 SMT 8 system around select_idle_core
> while running schbench shows us
>
> (units are in ticks, hence lesser is better)
> Without patch
> N Min Max Median Avg Stddev
> x 130 151 1083 284 322.72308 144.41494
>
>
> With patch
> N Min Max Median Avg Stddev Improvement
> x 164 88 610 201 225.79268 106.78943 30.03%
>
>
> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
I'm a bit surprised to not see this in linux-next or tip. Did this get
rejected or did it accidentally get overlooked because the subject is so
similar to 60588bfa223f ("sched/fair: Optimize select_idle_cpu") ?
--
Mel Gorman
SUSE Labs
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] sched/fair: Optimize select_idle_core
2020-01-22 13:55 ` Mel Gorman
@ 2020-01-22 14:22 ` Valentin Schneider
0 siblings, 0 replies; 5+ messages in thread
From: Valentin Schneider @ 2020-01-22 14:22 UTC (permalink / raw)
To: Mel Gorman, Srikar Dronamraju
Cc: Ingo Molnar, Peter Zijlstra, LKML, Rik van Riel, Thomas Gleixner,
Vincent Guittot
On 22/01/2020 13:55, Mel Gorman wrote:
>
> Acked-by: Mel Gorman <mgorman@techsingularity.net>
>
> I'm a bit surprised to not see this in linux-next or tip. Did this get
> rejected or did it accidentally get overlooked because the subject is so
> similar to 60588bfa223f ("sched/fair: Optimize select_idle_cpu") ?
>
Most likely the latter; I also had completely forgotten about it and had to
retrace where and when I reviewed that...
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] sched/fair: Optimize select_idle_core
2019-12-06 17:24 [PATCH v2] sched/fair: Optimize select_idle_core Srikar Dronamraju
2020-01-22 13:55 ` Mel Gorman
@ 2020-01-24 13:32 ` Srikar Dronamraju
2020-01-29 11:32 ` [tip: sched/core] sched/fair: Optimize select_idle_core() tip-bot2 for Srikar Dronamraju
2 siblings, 0 replies; 5+ messages in thread
From: Srikar Dronamraju @ 2020-01-24 13:32 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra
Cc: LKML, Mel Gorman, Rik van Riel, Thomas Gleixner,
Valentin Schneider, Vincent Guittot
Hey Peter, Ingo,
* Srikar Dronamraju <srikar@linux.vnet.ibm.com> [2019-12-06 22:54:22]:
> Currently we loop through all threads of a core to evaluate if the core is
> idle or not. This is unnecessary. If a thread of a core is not idle, skip
> evaluating other threads of a core. Also while clearing the cpumask, bits
> of all CPUs of a core can be cleared in one-shot.
>
> Collecting ticks on a Power 9 SMT 8 system around select_idle_core
> while running schbench shows us
>
> (units are in ticks, hence lesser is better)
> Without patch
> N Min Max Median Avg Stddev
> x 130 151 1083 284 322.72308 144.41494
>
>
> With patch
> N Min Max Median Avg Stddev Improvement
> x 164 88 610 201 225.79268 106.78943 30.03%
>
>
> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> ---
> Changelog v1->v2:
> Updated patch description with measurements made from a debug patch.
>
> kernel/sched/fair.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
Do you have any comments or improvements to be done for this patch?
--
Thanks and Regards
Srikar Dronamraju
^ permalink raw reply [flat|nested] 5+ messages in thread
* [tip: sched/core] sched/fair: Optimize select_idle_core()
2019-12-06 17:24 [PATCH v2] sched/fair: Optimize select_idle_core Srikar Dronamraju
2020-01-22 13:55 ` Mel Gorman
2020-01-24 13:32 ` Srikar Dronamraju
@ 2020-01-29 11:32 ` tip-bot2 for Srikar Dronamraju
2 siblings, 0 replies; 5+ messages in thread
From: tip-bot2 for Srikar Dronamraju @ 2020-01-29 11:32 UTC (permalink / raw)
To: linux-tip-commits
Cc: Srikar Dronamraju, Peter Zijlstra (Intel),
Ingo Molnar, Valentin Schneider, Vincent Guittot, Mel Gorman,
x86, LKML
The following commit has been merged into the sched/core branch of tip:
Commit-ID: bec2860a2bd6cd38ea34434d04f4033eb32f0f31
Gitweb: https://git.kernel.org/tip/bec2860a2bd6cd38ea34434d04f4033eb32f0f31
Author: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
AuthorDate: Fri, 06 Dec 2019 22:54:22 +05:30
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 28 Jan 2020 21:37:08 +01:00
sched/fair: Optimize select_idle_core()
Currently we loop through all threads of a core to evaluate if the core is
idle or not. This is unnecessary. If a thread of a core is not idle, skip
evaluating other threads of a core. Also while clearing the cpumask, bits
of all CPUs of a core can be cleared in one-shot.
Collecting ticks on a Power 9 SMT 8 system around select_idle_core
while running schbench shows us
(units are in ticks, hence lesser is better)
Without patch
N Min Max Median Avg Stddev
x 130 151 1083 284 322.72308 144.41494
With patch
N Min Max Median Avg Stddev Improvement
x 164 88 610 201 225.79268 106.78943 30.03%
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: https://lkml.kernel.org/r/20191206172422.6578-1-srikar@linux.vnet.ibm.com
---
kernel/sched/fair.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 25dffc0..1a0ce83 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5787,10 +5787,12 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
bool idle = true;
for_each_cpu(cpu, cpu_smt_mask(core)) {
- __cpumask_clear_cpu(cpu, cpus);
- if (!available_idle_cpu(cpu))
+ if (!available_idle_cpu(cpu)) {
idle = false;
+ break;
+ }
}
+ cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
if (idle)
return core;
^ permalink raw reply related [flat|nested] 5+ messages in thread
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Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2019-12-06 17:24 [PATCH v2] sched/fair: Optimize select_idle_core Srikar Dronamraju
2020-01-22 13:55 ` Mel Gorman
2020-01-22 14:22 ` Valentin Schneider
2020-01-24 13:32 ` Srikar Dronamraju
2020-01-29 11:32 ` [tip: sched/core] sched/fair: Optimize select_idle_core() tip-bot2 for Srikar Dronamraju
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