Messages in this thread Patch in this message | | | Date | Wed, 11 Dec 2019 20:16:50 +0800 | From | Peng Wang <> | Subject | Re: [PATCH] schied/fair: Skip updating "contrib" without load |
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On Mon, Dec 09, 2019 at 05:16:27PM +0100, Peter Zijlstra wrote: > On Sat, Dec 07, 2019 at 12:14:22AM +0800, Peng Wang wrote: > > We only update load_sum/runnable_load_sum/util_sum with > > decayed old sum when load is clear. > > What you're saying is that 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.
Yes.
> > I suppose that is so. did you happen to have performance numbers? Also, > I'm thinking this wants a comment.
Actually I don't know how to get the exact performance data. But I 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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