Messages in this thread | | | From | Josh Don <> | Date | Tue, 28 Jun 2022 17:41:06 -0700 | Subject | Re: [PATCH v4 4/7] sched/fair: remove useless check in select_idle_core |
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On Mon, Jun 27, 2022 at 8:51 PM Abel Wu <wuyun.abel@bytedance.com> wrote: > > > On 6/28/22 7:42 AM, Josh Don Wrote: > > On Sun, Jun 19, 2022 at 5:05 AM Abel Wu <wuyun.abel@bytedance.com> wrote: > >> > >> The function only gets called when sds->has_idle_cores is true which can > >> be possible only when sched_smt_present is enabled. > >> > >> Signed-off-by: Abel Wu <wuyun.abel@bytedance.com> > >> --- > >> kernel/sched/fair.c | 3 --- > >> 1 file changed, 3 deletions(-) > >> > >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > >> index aba1dad19574..1cc86e76e38e 100644 > >> --- a/kernel/sched/fair.c > >> +++ b/kernel/sched/fair.c > >> @@ -6256,9 +6256,6 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu > >> bool idle = true; > >> int cpu; > >> > >> - if (!static_branch_likely(&sched_smt_present)) > >> - return __select_idle_cpu(core, p); > >> - > > > > The static branch is basically free; although you're right that we > > currently don't take !smt_present branch direction here, it doesn't > > seem harmful to leave this check in case assumptions change about when > > we call select_idle_core(). > > I was thinking that it would be better to align with select_idle_smt > that the caller do the check if necessary.
The difference there though is that select_idle_smt() is called directly under the sched_smt_active() check, whereas the select_idle_core() is a few nested function calls away (and relies on has_idle_core rather than sched_smt_active() directly). So it is a bit harder to codify this expectation. Since we're using a static_branch here, I don't see a strong reason to remove it.
> > > >> for_each_cpu(cpu, cpu_smt_mask(core)) { > >> if (!available_idle_cpu(cpu)) { > >> idle = false; > >> -- > >> 2.31.1 > >>
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