Hi Vicent, On 2020/9/24 21:09, Vincent Guittot wrote: >>>> >>>> Would you mind share uperf(netperf load) result on your side? That's the >>>> workload I have seen the most benefit this patch contributed under heavy >>>> load level. >>> >>> with uperf, i've got the same kind of result as sched pipe >>> tip/sched/core: Throughput 24.83Mb/s (+/- 0.09%) >>> with this patch: Throughput 19.02Mb/s (+/- 0.71%) which is a 23% >>> regression as for sched pipe >>> >> In case this is caused by the logic error in this patch(sorry again), did >> you see any improvement in patch V2? Though it does not helps for nohz=off >> case, just want to know if it helps or does not help at all on arm platform. > > With the v2 which rate limit the update of the cpumask (but doesn't > support sched_idle stask), I don't see any performance impact:
I agree we should go the way with cpumask update rate limited. And I think no performance impact for sched-pipe is expected, as this workload has only 2 threads and the platform has 8 cores, so mostly previous cpu is returned, and even if select_idle_sibling is called, select_idle_core is hit and rarely call select_idle_cpu. But I'm more curious why there is 23% performance penalty? So for this patch, if you revert this change but keep cpumask updated, is 23% penalty still there? - cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); + cpumask_and(cpus, sds_idle_cpus(sd->shared), p->cpus_ptr); I just wonder if it's caused by the atomic ops as you have two cache domains with sd_llc(?). Do you have a x86 machine to make a comparison? It's hard for me to find an ARM machine but I'll try. Also, for uperf(task thread num = cpu num) workload, how is it on patch v2? no any performance impact? Thanks, -Aubrey
