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Date: Mon, 12 Sep 2022 10:44:15 +0200 From: Dietmar Eggemann <dietmar.eggemann@....com> To: Vincent Guittot <vincent.guittot@...aro.org>, mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com, rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com, linux-kernel@...r.kernel.org Cc: zhangqiao22@...wei.com Subject: Re: [PATCH 1/4] sched/fair: make sure to try to detach at least one movable task On 25/08/2022 14:27, Vincent Guittot wrote: s/sched/fair: make/sched/fair: Make > During load balance, we try at most env->loop_max time to move a task. > But it can happen that the loop_max LRU tasks (ie tail of > the cfs_tasks list) can't be moved to dst_cpu because of affinity. > In this case, loop in the list until we found at least one. > > The maximum of detached tasks remained the same as before. Not sure how this relates to the patch? Isn't this given by the `env->imbalance <= 0` check at the end of detach_tasks()? > > Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org> > --- > kernel/sched/fair.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index da388657d5ac..02b7b808e186 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8052,8 +8052,12 @@ static int detach_tasks(struct lb_env *env) > p = list_last_entry(tasks, struct task_struct, se.group_node); > > env->loop++; > - /* We've more or less seen every task there is, call it quits */ > - if (env->loop > env->loop_max) > + /* > + * We've more or less seen every task there is, call it quits I never understood this `more or less`. Either we have seen all tasks or not? > + * unless we haven't found any movable task yet. > + */ > + if (env->loop > env->loop_max && > + !(env->flags & LBF_ALL_PINNED)) > break; > > /* take a breather every nr_migrate tasks */ > @@ -10182,7 +10186,9 @@ static int load_balance(int this_cpu, struct rq *this_rq, > > if (env.flags & LBF_NEED_BREAK) { > env.flags &= ~LBF_NEED_BREAK; > - goto more_balance; > + /* Stop if we tried all running tasks */ Would say s/running/runnable but I see that we do use running/runnable interchangeably. > + if (env.loop < busiest->nr_running) > + goto more_balance; > } > > /* IMHO, there will be some interaction with the `All tasks on this runqueue were pinned by CPU affinity` check at the end of load_balance()?
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