Messages in this thread Patch in this message | | | From | Peng Wang <> | Subject | [PATCH v2] schied/fair: Skip calculating @contrib without load | Date | Fri, 13 Dec 2019 11:45:40 +0800 |
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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> --- kernel/sched/pelt.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c index a96db50..4392953 100644 --- a/kernel/sched/pelt.c +++ b/kernel/sched/pelt.c @@ -129,8 +129,9 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3) * Step 2 */ delta %= 1024; - contrib = __accumulate_pelt_segments(periods, - 1024 - sa->period_contrib, delta); + if (load) + contrib = __accumulate_pelt_segments(periods, + 1024 - sa->period_contrib, delta); } sa->period_contrib = delta; -- 1.8.3.1
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