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From: Jens Axboe <axboe@kernel.dk>
To: Boaz Harrosh <boaz@plexistor.com>, Phil Auld <pauld@redhat.com>,
	Ming Lei <ming.lei@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>,
	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 09:19:29 -0700
Message-ID: <8c02ab43-3880-68db-f293-9958510fb29e@kernel.dk> (raw)
In-Reply-To: <93de0f75-3664-c71e-9947-5b37ae935ddc@plexistor.com>

On 11/21/19 8:02 AM, Boaz Harrosh wrote:
> On 21/11/2019 16:12, Phil Auld wrote:
> <>
>>
>> The scheduler doesn't know if the queued_work submitter is going to go to sleep.
>> That's why I was singling out AIO. My understanding of it is that you submit the IO
>> and then keep going. So in that case it might be better to pick a node-local nearby
>> cpu instead. But this is a user of work queue issue not a scheduler issue.
>>
> 
> We have a very similar long standing problem in our system (zufs), that we had to do
> hacks to fix.
> 
> We have seen these CPU bouncing exacly as above in fio and more
> benchmarks, Our final analysis was:
>
> One thread is in wait_event() if the wake_up() is on the same CPU as
> the waiter, on some systems usually real HW and not VMs, would bounce
> to a different CPU.  Now our system has an array of worker-threads
> bound to each CPU. an incoming thread chooses a corresponding cpu
> worker-thread, let it run, waiting for a reply, then when the
> worker-thread is done it will do a wake_up(). Usually its fine and the
> wait_event() stays on the same CPU. But on some systems it will wakeup
> in a different CPU.
> 
> Now this is a great pity because in our case and the work_queue case
> and high % of places the thread calling wake_up() will then
> immediately go to sleep on something.  (Work done lets wait for new
> work)
> 
> I wish there was a flag to wake_up() or to the event object that says
> to relinquish the remaning of the time-slice to the waiter on same
> CPU, since I will be soon sleeping.

Isn't that basically what wake_up_sync() is?

-- 
Jens Axboe


  reply index

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-14 11:31 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 [this message]
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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