From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, tj@kernel.org,
sargun@sargun.me, xiexiuqi@huawei.com, xiezhipeng1@huawei.com,
torvalds@linux-foundation.org
Subject: Re: [PATCH 1/2] sched/fair: optimization of update_blocked_averages()
Date: Fri, 8 Feb 2019 17:30:58 +0100 [thread overview]
Message-ID: <20190208163058.GL32511@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1549469662-13614-2-git-send-email-vincent.guittot@linaro.org>
On Wed, Feb 06, 2019 at 05:14:21PM +0100, Vincent Guittot wrote:
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -346,6 +346,18 @@ static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
> static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
> {
> if (cfs_rq->on_list) {
> + struct rq *rq = rq_of(cfs_rq);
> +
> + /*
> + * With cfs_rq being unthrottled/throttled during an enqueue,
> + * it can happen the tmp_alone_branch points the a leaf that
> + * we finally want to del. In this case, tmp_alone_branch moves
> + * to the prev element but it will point to rq->leaf_cfs_rq_list
> + * at the end of the enqueue.
> + */
> + if (rq->tmp_alone_branch == &cfs_rq->leaf_cfs_rq_list)
> + rq->tmp_alone_branch = cfs_rq->leaf_cfs_rq_list.prev;
> +
> list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
> cfs_rq->on_list = 0;
> }
So that is:
enqueue_task_fair()
enqueue_entity()
list_add_lead_cfs_rq()
check_enqueue_throttle()
throttle_cfs_rq()
walk_tg_tree_from()
tg_throttle_down()
list_del_leaf_cfs_rq()
Which can try and remove a cfs_rq which we just added.
And because the list is a bottom-up order, and the deletion is a
downward operation, we must go back (prev) in the list.
So far so good I suppose.
> @@ -4449,8 +4465,10 @@ static int tg_throttle_down(struct task_group *tg, void *data)
> struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
>
> /* group is entering throttled state, stop time */
> - if (!cfs_rq->throttle_count)
> + if (!cfs_rq->throttle_count) {
> cfs_rq->throttled_clock_task = rq_clock_task(rq);
> + list_del_leaf_cfs_rq(cfs_rq);
> + }
> cfs_rq->throttle_count++;
>
> return 0;
next prev parent reply other threads:[~2019-02-08 16:31 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-06 16:14 [PATCH 0/2] sched/fair: Fix O(nr_cgroups) in load balance path Vincent Guittot
2019-02-06 16:14 ` [PATCH 1/2] sched/fair: optimization of update_blocked_averages() Vincent Guittot
2019-02-08 15:40 ` Peter Zijlstra
2019-02-08 15:44 ` Vincent Guittot
2019-02-08 16:30 ` Peter Zijlstra
2019-02-08 16:47 ` Vincent Guittot
2019-02-08 16:51 ` Peter Zijlstra
2019-02-08 16:51 ` Vincent Guittot
2019-02-08 16:30 ` Peter Zijlstra [this message]
2019-02-08 16:48 ` Vincent Guittot
2019-02-11 10:47 ` [tip:sched/core] sched/fair: Optimize update_blocked_averages() tip-bot for Vincent Guittot
2019-02-06 16:14 ` [PATCH 2/2] sched/fair: Fix O(nr_cgroups) in load balance path Vincent Guittot
2019-02-11 10:48 ` [tip:sched/core] sched/fair: Fix O(nr_cgroups) in the load balancing path tip-bot for Vincent Guittot
2019-02-06 16:23 ` [PATCH 0/2] sched/fair: Fix O(nr_cgroups) in load balance path Vincent Guittot
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