Messages in this thread | | | Subject | Re: [PATCH v2] sched/fair: Optimize select_idle_cpu | From | Valentin Schneider <> | Date | Fri, 13 Dec 2019 11:48:20 +0000 |
| |
On 13/12/2019 02:45, Cheng Jian wrote: > select_idle_cpu() will scan the LLC domain for idle CPUs, > it's always expensive. so the next commit : > > 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()") > > introduces a way to limit how many CPUs we scan. > > But it consume some CPUs out of 'nr' that are not allowed > for the task and thus waste our attempts. The function > always return nr_cpumask_bits, and we can't find a CPU > which our task is allowed to run. > > Cpumask may be too big, similar to select_idle_core(), use > per_cpu_ptr 'select_idle_mask' to prevent stack overflow. > > Fixes: 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()") > Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
> --- > kernel/sched/fair.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 08a233e97a01..d48244388ce9 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5828,6 +5828,7 @@ 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 +5860,11 @@ 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)) >
| |