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From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dave Chinner <david@fromorbit.com>,
	Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
	Phil Auld <pauld@redhat.com>, Ming Lei <ming.lei@redhat.com>,
	linux-block <linux-block@vger.kernel.org>,
	linux-fs <linux-fsdevel@vger.kernel.org>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	linux-kernel <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>
Subject: Re: [PATCH v4] sched/core: Preempt current task in favour of bound kthread
Date: Thu, 12 Dec 2019 14:12:47 +0100
Message-ID: <20191212131247.GY2827@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAKfTPtCUm5vuvNiWszJ5tWHxmcZ2v_KexOxnBHLUkBcqC-P3fw@mail.gmail.com>

On Thu, Dec 12, 2019 at 12:20:01PM +0100, Vincent Guittot wrote:
> On Thu, 12 Dec 2019 at 11:23, Peter Zijlstra <peterz@infradead.org> wrote:

> > Just for giggles, that'd look something like:
> >
> >         while (!entity_is_task(se) {
> >                 cfs_rq = group_cfs_rq(se);
> >                 se = pick_next_entity(cfs_rq, cfs_rq->curr);
> >         }
> >         p = task_of(se);
> >
> >         if (is_per_cpu_kthread(p))
> >                 ideal_runtime /= 2;
> >
> > the core-scheduling patch set includes the right primitive for this I
> > think, pick_task_fair().
> 
> why not only updating wan_gran() which is the only function which uses
> sysctl_sched_wakeup_granularity ?

I don't see how, it works on se, which need not be a task.

> For per cpu kthread, we could set the gran to sched_min_granularity
> instead of scaling it with thread's priority so per cpu kthread can
> still preempt current ask even if sysctl_sched_wakeup_granularity is
> large

Also, we're not poking at wakeup preemption anymore. That, as explained
by Dave, is not the right thing to do. What we want instead is to make
tick preemption a little more agressive.

And tick based preemption currently purely looks at the leftmost entity
for each runqueue we find while iterating current. IE, it might never
even see the task we tagged with next.

Also, did I say I hates cgroups :-)

  reply index

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
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 [this message]
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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