On 16/06/20 17:48, peter.pu...@linaro.org wrote: > From: Peter Puhov <peter.pu...@linaro.org> > We tested this patch with following benchmarks: > perf bench -f simple sched pipe -l 4000000 > perf bench -f simple sched messaging -l 30000 > perf bench -f simple mem memset -s 3GB -l 15 -f default > perf bench -f simple futex wake -s -t 640 -w 1 > sysbench cpu --threads=8 --cpu-max-prime=10000 run > sysbench memory --memory-access-mode=rnd --threads=8 run > sysbench threads --threads=8 run > sysbench mutex --mutex-num=1 --threads=8 run > hackbench --loops 20000 > hackbench --pipe --threads --loops 20000 > hackbench --pipe --threads --loops 20000 --datasize 4096 > > and found some performance improvements in: > sysbench threads > sysbench mutex > perf bench futex wake > and no regressions in others. >
One nitpick for the results of those: condensing them in a table form would make them more reader-friendly. Perhaps something like: | Benchmark | Metric | Lower is better? | BASELINE | SERIES | DELTA | |------------------+----------+------------------+----------+--------+-------| | Sysbench threads | # events | No | 45526 | 56567 | +24% | | Sysbench mutex | ... | | | | | If you want to include more stats for each benchmark, you could have one table per (e.g. see [1]) - it'd still be a more readable form (or so I believe). [1]: https://lore.kernel.org/lkml/20200206191957.12325-1-valentin.schnei...@arm.com/ > --- > kernel/sched/fair.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 02f323b85b6d..abcbdf80ee75 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8662,8 +8662,14 @@ static bool update_pick_idlest(struct sched_group > *idlest, > > case group_has_spare: > /* Select group with most idle CPUs */ > - if (idlest_sgs->idle_cpus >= sgs->idle_cpus) > + if (idlest_sgs->idle_cpus > sgs->idle_cpus) > return false; > + > + /* Select group with lowest group_util */ > + if (idlest_sgs->idle_cpus == sgs->idle_cpus && > + idlest_sgs->group_util <= sgs->group_util) > + return false; > + > break; > } update_sd_pick_busiest() uses the group's nr_running instead. You mention in the changelog that using nr_running is a possible alternative, did you try benchmarking that and seeing how it compares to using group_util? I think it would be nice to keep pick_busiest() and pick_idlest() aligned wherever possible/sensible. Also, there can be cases where one group has a few "big" tasks and another has a handful more "small" tasks. Say something like sgs_a->group_util = U sgs_a->sum_nr_running = N sgs_b->group_util = U*4/3 sgs_b->sum_nr_running = N*2/3 (sgs_b has more util per task, i.e. bigger tasks on average) Given that we're in the 'group_has_spare' case, I would think picking the group with the lesser amount of running tasks would make sense. Though I guess you can find pathological cases where the util per task difference is huge and we should look at util first...
