Messages in this thread | | | Subject | Re: [PATCH] sched/fair: Optimize select_idle_cpu | From | "chengjian (D)" <> | Date | Fri, 13 Dec 2019 17:57:15 +0800 |
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On 2019/12/12 23:24, Peter Zijlstra wrote: > On Thu, Dec 12, 2019 at 10:41:02PM +0800, Cheng Jian wrote: > >> Fixes: 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()") > The 'funny' thing is that select_idle_core() actually does the right > thing. > > Copying that should work: > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 08a233e97a01..416d574dcebf 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5828,6 +5837,7 @@ static inline int select_idle_smt(struct task_struct *p, int target) > */ > static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target) > { > + struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask); > struct sched_domain *this_sd; > u64 avg_cost, avg_idle; > u64 time, cost; > @@ -5859,11 +5869,11 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t > > time = cpu_clock(this); > > - for_each_cpu_wrap(cpu, sched_domain_span(sd), target) { > + cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); > + > + for_each_cpu_wrap(cpu, cpus, target) { > if (!--nr) > return si_cpu; > - if (!cpumask_test_cpu(cpu, p->cpus_ptr)) > - continue; > if (available_idle_cpu(cpu)) > break; > if (si_cpu == -1 && sched_idle_cpu(cpu)) > > .
in select_idle_smt()
/* * Scan the local SMT mask for idle CPUs. */ static int select_idle_smt(struct task_struct *p, int target) { int cpu, si_cpu = -1;
if (!static_branch_likely(&sched_smt_present)) return -1;
for_each_cpu(cpu, cpu_smt_mask(target)) { if (!cpumask_test_cpu(cpu, p->cpus_ptr)) continue; if (available_idle_cpu(cpu)) return cpu; if (si_cpu == -1 && sched_idle_cpu(cpu)) si_cpu = cpu; }
return si_cpu; }
Why don't we do the same thing in this function,
although cpu_smt_present () often has few CPUs.
it is better to determine the 'p->cpus_ptr' first.
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