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From: Ming Lei <ming.lei@redhat.com>
To: Phil Auld <pauld@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Dave Chinner <david@fromorbit.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: single aio thread is migrated crazily by scheduler
Date: Thu, 21 Nov 2019 12:12:18 +0800	[thread overview]
Message-ID: <20191121041218.GK24548@ming.t460p> (raw)
In-Reply-To: <20191120220313.GC18056@pauld.bos.csb>

On Wed, Nov 20, 2019 at 05:03:13PM -0500, Phil Auld wrote:
> Hi Peter,
> 
> On Wed, Nov 20, 2019 at 08:16:36PM +0100 Peter Zijlstra wrote:
> > On Tue, Nov 19, 2019 at 07:40:54AM +1100, Dave Chinner wrote:
> > > On Mon, Nov 18, 2019 at 10:21:21AM +0100, Peter Zijlstra wrote:
> > 
> > > > We typically only fall back to the active balancer when there is
> > > > (persistent) imbalance and we fail to migrate anything else (of
> > > > substance).
> > > > 
> > > > The tuning mentioned has the effect of less frequent scheduling, IOW,
> > > > leaving (short) tasks on the runqueue longer. This obviously means the
> > > > load-balancer will have a bigger chance of seeing them.
> > > > 
> > > > Now; it's been a while since I looked at the workqueue code but one
> > > > possible explanation would be if the kworker that picks up the work item
> > > > is pinned. That would make it runnable but not migratable, the exact
> > > > situation in which we'll end up shooting the current task with active
> > > > balance.
> > > 
> > > Yes, that's precisely the problem - work is queued, by default, on a
> > > specific CPU and it will wait for a kworker that is pinned to that
> > 
> > I'm thinking the problem is that it doesn't wait. If it went and waited
> > for it, active balance wouldn't be needed, that only works on active
> > tasks.
> 
> Since this is AIO I wonder if it should queue_work on a nearby cpu by 
> default instead of unbound.  

When the current CPU isn't busy enough, there is still cost for completing
request remotely.

Or could we change queue_work() in the following way?

 * We try to queue the work to the CPU on which it was submitted, but if the
 * CPU dies or is saturated enough it can be processed by another CPU.

Can we decide in a simple or efficient way if the current CPU is saturated
enough?

Thanks,
Ming


  reply	other threads:[~2019-11-21  4:12 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 [this message]
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
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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