From: Peter Zijlstra <peterz@infradead.org>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Dave Chinner <david@fromorbit.com>, Phil Auld <pauld@redhat.com>,
Ming Lei <ming.lei@redhat.com>,
linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org,
Jeff Moyer <jmoyer@redhat.com>,
Dave Chinner <dchinner@redhat.com>,
Eric Sandeen <sandeen@redhat.com>, Christoph Hellwig <hch@lst.de>,
Jens Axboe <axboe@kernel.dk>, Ingo Molnar <mingo@redhat.com>,
Tejun Heo <tj@kernel.org>,
Vincent Guittot <vincent.guittot@linaro.org>
Subject: Re: [PATCH v2] sched/core: Preempt current task in favour of bound kthread
Date: Tue, 10 Dec 2019 10:26:01 +0100 [thread overview]
Message-ID: <20191210092601.GK2844@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20191210054330.GF27253@linux.vnet.ibm.com>
On Tue, Dec 10, 2019 at 11:13:30AM +0530, Srikar Dronamraju wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 44123b4d14e8..82126cbf62cd 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2664,7 +2664,12 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
> */
> int wake_up_process(struct task_struct *p)
> {
> - return try_to_wake_up(p, TASK_NORMAL, 0);
> + int wake_flags = 0;
> +
> + if (is_per_cpu_kthread(p))
> + wake_flags = WF_KTHREAD;
> +
> + return try_to_wake_up(p, TASK_NORMAL, wake_flags);
> }
> EXPORT_SYMBOL(wake_up_process);
Why wake_up_process() and not try_to_wake_up() ? This way
wake_up_state(.state = TASK_NORMAL() is no longer the same as
wake_up_process(), and that's weird!
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 69a81a5709ff..36486f71e59f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6660,6 +6660,27 @@ static void set_skip_buddy(struct sched_entity *se)
> cfs_rq_of(se)->skip = se;
> }
>
> +static int kthread_wakeup_preempt(struct rq *rq, struct task_struct *p, int wake_flags)
> +{
> + struct task_struct *curr = rq->curr;
> + struct cfs_rq *cfs_rq = task_cfs_rq(curr);
> +
> + if (!(wake_flags & WF_KTHREAD))
> + return 0;
> +
> + if (p->nr_cpus_allowed != 1 || curr->nr_cpus_allowed == 1)
> + return 0;
Per the above, WF_KTHREAD already implies p->nr_cpus_allowed == 1.
> + if (cfs_rq->nr_running > 2)
> + return 0;
> +
> + /*
> + * Don't preempt, if the waking kthread is more CPU intensive than
> + * the current thread.
> + */
> + return p->nvcsw * curr->nivcsw >= p->nivcsw * curr->nvcsw;
Both these conditions seem somewhat arbitrary. The number of context
switch does not correspond to CPU usage _at_all_.
vtime OTOH does reflect exactly that, if it runs a lot, it will be ahead
in the tree.
> +}
> +
> /*
> * Preempt the current task with a newly woken task if needed:
> */
> @@ -6716,7 +6737,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
> find_matching_se(&se, &pse);
> update_curr(cfs_rq_of(se));
> BUG_ON(!pse);
> - if (wakeup_preempt_entity(se, pse) == 1) {
> + if (wakeup_preempt_entity(se, pse) == 1 || kthread_wakeup_preempt(rq, p, wake_flags)) {
> /*
> * Bias pick_next to pick the sched entity that is
> * triggering this preemption.
How about something like:
if (wakeup_preempt_entity(se, pse) >= 1-!!(wake_flags & WF_KTHREAD))
instead? Then we allow kthreads a little more preemption room.
next prev parent reply other threads:[~2019-12-10 9:26 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-14 11:31 single aio thread is migrated crazily by scheduler Ming Lei
2019-11-14 13:14 ` Peter Zijlstra
2019-11-15 0:09 ` Ming Lei
2019-11-15 14:16 ` Ming Lei
2019-11-14 23:54 ` Dave Chinner
2019-11-15 1:08 ` Ming Lei
2019-11-15 4:56 ` Dave Chinner
2019-11-15 7:08 ` Ming Lei
2019-11-15 23:40 ` Dave Chinner
2019-11-16 6:31 ` Ming Lei
2019-11-18 9:21 ` Peter Zijlstra
2019-11-18 14:54 ` Vincent Guittot
2019-11-18 20:40 ` Dave Chinner
2019-11-20 19:16 ` Peter Zijlstra
2019-11-20 22:03 ` Phil Auld
2019-11-21 4:12 ` Ming Lei
2019-11-21 14:12 ` Phil Auld
2019-11-21 15:02 ` Boaz Harrosh
2019-11-21 16:19 ` Jens Axboe
2019-12-09 16:58 ` Srikar Dronamraju
2019-11-21 22:10 ` Dave Chinner
2019-11-21 13:29 ` Peter Zijlstra
2019-11-21 14:21 ` Phil Auld
2019-12-09 16:51 ` Srikar Dronamraju
2019-12-09 23:17 ` Dave Chinner
2019-12-10 3:27 ` Srikar Dronamraju
2019-12-10 5:43 ` [PATCH v2] sched/core: Preempt current task in favour of bound kthread Srikar Dronamraju
2019-12-10 9:26 ` Peter Zijlstra [this message]
2019-12-10 9:33 ` Peter Zijlstra
2019-12-10 10:18 ` Srikar Dronamraju
2019-12-10 10:16 ` Srikar Dronamraju
2019-12-10 9:43 ` Vincent Guittot
2019-12-10 10:11 ` Srikar Dronamraju
2019-12-10 11:02 ` Vincent Guittot
2019-12-10 17:23 ` [PATCH v3] " Srikar Dronamraju
2019-12-11 17:38 ` [PATCH v4] " Srikar Dronamraju
2019-12-11 22:46 ` Dave Chinner
2019-12-12 10:10 ` Peter Zijlstra
2019-12-12 10:14 ` Peter Zijlstra
2019-12-12 10:23 ` Peter Zijlstra
2019-12-12 11:20 ` Vincent Guittot
2019-12-12 13:12 ` Peter Zijlstra
2019-12-12 15:07 ` Srikar Dronamraju
2019-12-12 15:15 ` Peter Zijlstra
2019-12-13 5:32 ` Srikar Dronamraju
2019-11-18 16:26 ` single aio thread is migrated crazily by scheduler Srikar Dronamraju
2019-11-18 21:18 ` Dave Chinner
2019-11-19 8:54 ` Ming Lei
[not found] ` <20191128094003.752-1-hdanton@sina.com>
2019-11-28 9:53 ` Vincent Guittot
2019-12-02 2:46 ` Ming Lei
2019-12-02 4:02 ` Dave Chinner
2019-12-02 4:22 ` Ming Lei
2019-12-02 13:45 ` Vincent Guittot
2019-12-02 21:22 ` Phil Auld
2019-12-03 9:45 ` Vincent Guittot
2019-12-04 13:50 ` Ming Lei
2019-12-02 23:53 ` Dave Chinner
2019-12-03 0:18 ` Ming Lei
2019-12-03 13:34 ` Vincent Guittot
2019-12-02 7:39 ` Juri Lelli
2019-12-02 3:08 ` Dave Chinner
[not found] ` <20191202090158.15016-1-hdanton@sina.com>
2019-12-02 23:06 ` Dave Chinner
[not found] ` <20191203131514.5176-1-hdanton@sina.com>
2019-12-03 22:29 ` Dave Chinner
[not found] ` <20191204102903.896-1-hdanton@sina.com>
2019-12-04 22:59 ` Dave Chinner
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