Messages in this thread | | | Date | Tue, 23 Nov 2021 22:07:05 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] sched/fair: Remove the cost of a redundant cpumask_next_wrap in select_idle_cpu |
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On Tue, Nov 23, 2021 at 07:22:29PM +0800, Barry Song wrote: > From: Barry Song <song.bao.hua@hisilicon.com> > > This patch keeps the same scanning amount, but drops a redundant loop > of cpumask_next_wrap. > The original code did for_each_cpu_wrap(cpu, cpus, target + 1), then > checked --nr; this patch does --nr before doing the next loop, thus, > it can remove a cpumask_next_wrap() which costs a little bit. > > Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> > --- > kernel/sched/fair.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index ff69f24..e2fb3e0 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6298,9 +6298,9 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool > > span_avg = sd->span_weight * avg_idle; > if (span_avg > 4*avg_cost) > - nr = div_u64(span_avg, avg_cost); > + nr = div_u64(span_avg, avg_cost) - 1; > else > - nr = 4; > + nr = 3; > > time = cpu_clock(this); > } > @@ -6312,11 +6312,11 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool > return i; > > } else { > - if (!--nr) > - return -1; > idle_cpu = __select_idle_cpu(cpu, p); > if ((unsigned int)idle_cpu < nr_cpumask_bits) > break; > + if (!--nr) > + return -1; > } > }
That's just confusing code. Isn't it much clearer to write the whole thing like so ?
nr--; for_each_cpu_wrap(cpu, cpus, target+1) { ... if (!nr--) return -1; }
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