Messages in this thread Patch in this message | | | Date | Tue, 17 Dec 2019 12:39:52 -0000 | From | "tip-bot2 for Peng Wang" <> | Subject | [tip: sched/core] schied/fair: Skip calculating @contrib without load |
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The following commit has been merged into the sched/core branch of tip:
Commit-ID: d040e0734fb3dedfe24c3d94f5a32b4812eca610 Gitweb: https://git.kernel.org/tip/d040e0734fb3dedfe24c3d94f5a32b4812eca610 Author: Peng Wang <rocking@linux.alibaba.com> AuthorDate: Fri, 13 Dec 2019 11:45:40 +08:00 Committer: Peter Zijlstra <peterz@infradead.org> CommitterDate: Tue, 17 Dec 2019 13:32:51 +01:00
schied/fair: Skip calculating @contrib without load
Because of the:
if (!load) runnable = running = 0;
clause in ___update_load_sum(), all the actual users of @contrib in accumulate_sum():
if (load) sa->load_sum += load * contrib; if (runnable) sa->runnable_load_sum += runnable * contrib; if (running) sa->util_sum += contrib << SCHED_CAPACITY_SHIFT;
don't happen, and therefore we don't care what @contrib actually is and calculating it is pointless.
If we count the times when @load equals zero and not as below:
if (load) { load_is_not_zero_count++; contrib = __accumulate_pelt_segments(periods, 1024 - sa->period_contrib,delta); } else load_is_zero_count++;
As we can see, load_is_zero_count is much bigger than load_is_zero_count, and the gap is gradually widening:
load_is_zero_count: 6016044 times load_is_not_zero_count: 244316 times 19:50:43 up 1 min, 1 user, load average: 0.09, 0.06, 0.02
load_is_zero_count: 7956168 times load_is_not_zero_count: 261472 times 19:51:42 up 2 min, 1 user, load average: 0.03, 0.05, 0.01
load_is_zero_count: 10199896 times load_is_not_zero_count: 278364 times 19:52:51 up 3 min, 1 user, load average: 0.06, 0.05, 0.01
load_is_zero_count: 14333700 times load_is_not_zero_count: 318424 times 19:54:53 up 5 min, 1 user, load average: 0.01, 0.03, 0.00
Perhaps we can gain some performance advantage by saving these unnecessary calculation.
Signed-off-by: Peng Wang <rocking@linux.alibaba.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Vincent Guittot < vincent.guittot@linaro.org> Link: https://lkml.kernel.org/r/1576208740-35609-1-git-send-email-rocking@linux.alibaba.com --- kernel/sched/pelt.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c index a96db50..bd006b7 100644 --- a/kernel/sched/pelt.c +++ b/kernel/sched/pelt.c @@ -129,8 +129,20 @@ accumulate_sum(u64 delta, struct sched_avg *sa, * Step 2 */ delta %= 1024; - contrib = __accumulate_pelt_segments(periods, - 1024 - sa->period_contrib, delta); + if (load) { + /* + * This relies on the: + * + * if (!load) + * runnable = running = 0; + * + * clause from ___update_load_sum(); this results in + * the below usage of @contrib to dissapear entirely, + * so no point in calculating it. + */ + contrib = __accumulate_pelt_segments(periods, + 1024 - sa->period_contrib, delta); + } } sa->period_contrib = delta; @@ -205,7 +217,9 @@ ___update_load_sum(u64 now, struct sched_avg *sa, * This means that weight will be 0 but not running for a sched_entity * but also for a cfs_rq if the latter becomes idle. As an example, * this happens during idle_balance() which calls - * update_blocked_averages() + * update_blocked_averages(). + * + * Also see the comment in accumulate_sum(). */ if (!load) runnable = running = 0;
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