Messages in this thread | | | Date | Mon, 25 Dec 2023 16:17:49 +0100 | Subject | Re: [PATCH] sched/fair: Do not scan non-movable tasks several times | From | Konstantin Khorenko <> |
| |
On 18.12.2023 17:48, Vincent Guittot wrote: > On Thu, 14 Dec 2023 at 15:42, Konstantin Khorenko > <khorenko@virtuozzo.com> wrote: >> >> If busiest rq is small, nr_running < SCHED_NR_MIGRATE_BREAK and all >> tasks are not movable, detach_tasks() should not iterate more than tasks >> available in the busiest rq. >> >> Previously the (env->loop > env->loop_max) condition prevented us from > > It's usually better to give the commit directly when we know it : > Before commit : b0defa7ae03e ("sched/fair: Make sure to try to detach > at least one movable task"), > the (env->loop > env->loop_max) condition prevented us from ...
You are definitely right, added.
>> scanning non-movable tasks more than rq size times, but after we start >> checking the LBF_ALL_PINNED flag, the "all tasks are not movable" case >> is under threat. >> > > Fixes: b0defa7ae03e ("sched/fair: Make sure to try to detach at least > one movable task")
Added this too, thank you.
>> Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com> >> --- >> kernel/sched/fair.c | 7 ++++++- >> 1 file changed, 6 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index d7a3c63a2171..faa2a765e899 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -11219,7 +11219,6 @@ static int load_balance(int this_cpu, struct rq *this_rq, >> .dst_rq = this_rq, >> .dst_grpmask = group_balance_mask(sd->groups), >> .idle = idle, >> - .loop_break = SCHED_NR_MIGRATE_BREAK, >> .cpus = cpus, >> .fbq_type = all, >> .tasks = LIST_HEAD_INIT(env.tasks), >> @@ -11265,6 +11264,12 @@ static int load_balance(int this_cpu, struct rq *this_rq, >> * correctly treated as an imbalance. >> */ >> env.loop_max = min(sysctl_sched_nr_migrate, busiest->nr_running); >> + /* >> + * If busiest rq is small, nr_running < SCHED_NR_MIGRATE_BREAK >> + * and all tasks are not movable, detach_tasks() should not >> + * iterate more than tasks available in rq. >> + */ >> + env.loop_break = min(SCHED_NR_MIGRATE_BREAK, busiest->nr_running); > > Should it be after more_balance: ? > In case we do "more_balance:" on a new_dst_cpu and it ends up that > finally there is no more movable task as we released the lock of > busiest rq in the meantime ?
Well, both yes and no here. If we simply move the env.loop_break assignment after "more_balance" label, we will break the handling LBF_NEED_BREAK case.
But you are right, the new_dst_cpu case should also not just reset loop_break to SCHED_NR_MIGRATE_BREAK, but do the same min() calculation.
So i've added one more label before the env.loop_break = min(...) and used it in the new_dst_cpu case.
> Also you can remove one more superfluous init of loop_break:
Yep, dropped it, thank you.
> --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -11361,7 +11361,6 @@ static int load_balance(int this_cpu, struct > rq *this_rq, > */ > if (!cpumask_subset(cpus, env.dst_grpmask)) { > env.loop = 0; > - env.loop_break = SCHED_NR_MIGRATE_BREAK; > goto redo; > } > goto out_all_pinned; > >> >> more_balance: >> rq_lock_irqsave(busiest, &rf); >> -- >> 2.39.3 >>
| |