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Date: Tue, 25 Aug 2020 20:46:24 +0800 From: Jiang Biao <benbjiang@...il.com> To: Xunlei Pang <xlpang@...ux.alibaba.com> Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Vincent Guittot <vincent.guittot@...aro.org>, Juri Lelli <juri.lelli@...hat.com>, Wetp Zhang <wetp.zy@...ux.alibaba.com>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] sched/fair: Fix wrong cpu selecting from isolated domain On Tue, 25 Aug 2020 at 17:28, xunlei <xlpang@...ux.alibaba.com> wrote: > > On 2020/8/25 下午2:37, Jiang Biao wrote: > > On Mon, 24 Aug 2020 at 20:31, Xunlei Pang <xlpang@...ux.alibaba.com> wrote: > >> > >> We've met problems that occasionally tasks with full cpumask > >> (e.g. by putting it into a cpuset or setting to full affinity) > >> were migrated to our isolated cpus in production environment. > >> > >> After some analysis, we found that it is due to the current > >> select_idle_smt() not considering the sched_domain mask. > >> > >> Fix it by checking the valid domain mask in select_idle_smt(). > >> > >> Fixes: 10e2f1acd010 ("sched/core: Rewrite and improve select_idle_siblings()) > >> Reported-by: Wetp Zhang <wetp.zy@...ux.alibaba.com> > >> Signed-off-by: Xunlei Pang <xlpang@...ux.alibaba.com> > >> --- > >> kernel/sched/fair.c | 9 +++++---- > >> 1 file changed, 5 insertions(+), 4 deletions(-) > >> > >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > >> index 1a68a05..fa942c4 100644 > >> --- a/kernel/sched/fair.c > >> +++ b/kernel/sched/fair.c > >> @@ -6075,7 +6075,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int > >> /* > >> * Scan the local SMT mask for idle CPUs. > >> */ > >> -static int select_idle_smt(struct task_struct *p, int target) > >> +static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target) > >> { > >> int cpu; > >> > >> @@ -6083,7 +6083,8 @@ static int select_idle_smt(struct task_struct *p, int target) > >> return -1; > >> > >> for_each_cpu(cpu, cpu_smt_mask(target)) { > >> - if (!cpumask_test_cpu(cpu, p->cpus_ptr)) > >> + if (!cpumask_test_cpu(cpu, p->cpus_ptr) || > >> + !cpumask_test_cpu(cpu, sched_domain_span(sd))) > > Maybe the following change could be better, :) > > for_each_cpu_and(cpu, cpu_smt_mask(target), sched_domain_span(sd)) > > keep a similar style with select_idle_core/cpu, and could reduce loops. > > > > I thought that, but given that smt mask is usually small, the original > code may run a bit faster? Not sure. :) It's OK for me. Regards, Jiang
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