Messages in this thread | | | Subject | Re: [PATCH v3 3/7] sched: rotate the cpu search window for better spread | From | Subhra Mazumdar <> | Date | Fri, 28 Jun 2019 15:34:25 -0700 |
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On 6/28/19 4:54 AM, Srikar Dronamraju wrote: > * subhra mazumdar <subhra.mazumdar@oracle.com> [2019-06-26 18:29:15]: > >> Rotate the cpu search window for better spread of threads. This will ensure >> an idle cpu will quickly be found if one exists. > While rotating the cpu search window is good, not sure if this can find a > idle cpu quickly. The probability of finding an idle cpu still should remain > the same. No? > >> Signed-off-by: subhra mazumdar <subhra.mazumdar@oracle.com> >> --- >> kernel/sched/fair.c | 10 ++++++++-- >> 1 file changed, 8 insertions(+), 2 deletions(-) >> >> @@ -6219,9 +6219,15 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t >> } >> } >> >> + if (per_cpu(next_cpu, target) != -1) >> + target_tmp = per_cpu(next_cpu, target); >> + else >> + target_tmp = target; >> + >> time = local_clock(); >> >> - for_each_cpu_wrap(cpu, sched_domain_span(sd), target) { >> + for_each_cpu_wrap(cpu, sched_domain_span(sd), target_tmp) { >> + per_cpu(next_cpu, target) = cpu; > Shouldn't this assignment be outside the for loop. > With the current code, > 1. We keep reassigning multiple times. > 2. The last assignment happes for idle_cpu and sometimes the > assignment is for non-idle cpu. We want the last assignment irrespective of it was an idle cpu or not since in both cases we want to track the boundary of search.
Thanks, Subhra
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