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From: Jens Axboe <axboe@kernel.dk>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Carter Li 李通洲" <carter.li@eoitek.com>,
	"Pavel Begunkov" <asml.silence@gmail.com>,
	io-uring <io-uring@vger.kernel.org>
Subject: Re: [ISSUE] The time cost of IOSQE_IO_LINK
Date: Fri, 14 Feb 2020 09:18:34 -0700
Message-ID: <7c4c3996-4886-eb58-cdee-fe0951907ab5@kernel.dk> (raw)
In-Reply-To: <5995f84e-8a6c-e774-6bb5-5b9b87a9cd3c@kernel.dk>

On 2/14/20 8:47 AM, Jens Axboe wrote:
>> I suspect you meant to put that in finish_task_switch() which is the
>> tail end of every schedule(), schedule_tail() is the tail end of
>> clone().
>>
>> Or maybe you meant to put it in (and rename) sched_update_worker() which
>> is after every schedule() but in a preemptible context -- much saner
>> since you don't want to go add an unbounded amount of work in a
>> non-preemptible context.
>>
>> At which point you already have your callback: io_wq_worker_running(),
>> or is this for any random task?
> 
> Let me try and clarify - this isn't for the worker tasks, this is for
> any task that is using io_uring. In fact, it's particularly not for the
> worker threads, just the task itself.
> 
> I basically want the handler to be called when:
> 
> 1) The task is scheduled in. The poll will complete and stuff some items
>    on that task list, and I want to task to process them as it wakes up.
> 
> 2) The task is going to sleep, don't want to leave entries around while
>    the task is sleeping.
> 
> 3) I need it to be called from "normal" context, with ints enabled,
>    preempt enabled, etc.
> 
> sched_update_worker() (with a rename) looks ideal for #1, and the
> context is sane for me. Just need a good spot to put the hook call for
> schedule out. I think this:
> 
> 	if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
> 		preempt_disable();
> 		if (tsk->flags & PF_WQ_WORKER)
> 			wq_worker_sleeping(tsk);
> 		else
> 			io_wq_worker_sleeping(tsk);
> 		preempt_enable_no_resched();
> 	}
> 
> just needs to go into another helper, and then I can call it there
> outside of the preempt.
> 
> I'm sure there are daemons lurking here, but I'll test and see how it
> goes...

Here's a stab at cleaning it up:

https://git.kernel.dk/cgit/linux-block/log/?h=io_uring-task-poll

top two patches. First one simply cleans up the sched_update_worker(),
so we now have sched_in_update() and sched_out_update(). No changes in
this patch, just moves the worker sched-out handling into a helper.

2nd patch then utilizes this to flush the per-task requests that may
have been queued up.

-- 
Jens Axboe


  reply index

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12 16:31 Carter Li 李通洲
2020-02-12 17:11 ` Jens Axboe
2020-02-12 17:22   ` Jens Axboe
2020-02-12 17:29     ` Jens Axboe
2020-02-13  0:33   ` Carter Li 李通洲
2020-02-13 15:08     ` Pavel Begunkov
2020-02-13 15:14       ` Jens Axboe
2020-02-13 15:51         ` Carter Li 李通洲
2020-02-14  1:25           ` Carter Li 李通洲
2020-02-14  2:45             ` Jens Axboe
2020-02-14  5:03               ` Jens Axboe
2020-02-14 15:32                 ` Peter Zijlstra
2020-02-14 15:47                   ` Jens Axboe
2020-02-14 16:18                     ` Jens Axboe [this message]
2020-02-14 17:52                       ` Jens Axboe
2020-02-14 20:44                         ` Jens Axboe
2020-02-15  0:16                           ` Carter Li 李通洲
2020-02-15  1:10                             ` Jens Axboe
2020-02-15  1:25                               ` Carter Li 李通洲
2020-02-15  1:27                                 ` Jens Axboe
2020-02-15  6:01                                   ` Jens Axboe
2020-02-15  6:32                                     ` Carter Li 李通洲
2020-02-15 15:11                                       ` Jens Axboe
2020-02-16 19:06                                     ` Pavel Begunkov
2020-02-16 22:23                                       ` Jens Axboe
2020-02-17 10:30                                         ` Pavel Begunkov
2020-02-17 19:30                                           ` Jens Axboe
2020-02-16 23:06                                       ` Jens Axboe
2020-02-16 23:07                                         ` Jens Axboe
2020-02-17 12:09                           ` Peter Zijlstra
2020-02-17 16:12                             ` Jens Axboe
2020-02-17 17:16                               ` Jens Axboe
2020-02-17 17:46                                 ` Peter Zijlstra
2020-02-17 18:16                                   ` Jens Axboe
2020-02-18 13:13                                     ` Peter Zijlstra
2020-02-18 14:27                                       ` [PATCH] asm-generic/atomic: Add try_cmpxchg() fallbacks Peter Zijlstra
2020-02-18 14:40                                         ` Peter Zijlstra
2020-02-20 10:30                                         ` Will Deacon
2020-02-20 10:37                                           ` Peter Zijlstra
2020-02-20 10:39                                             ` Will Deacon
2020-02-18 14:56                                       ` [ISSUE] The time cost of IOSQE_IO_LINK Oleg Nesterov
2020-02-18 15:07                                         ` Oleg Nesterov
2020-02-18 15:38                                           ` Peter Zijlstra
2020-02-18 16:33                                             ` Jens Axboe
2020-02-18 15:07                                         ` Peter Zijlstra
2020-02-18 15:50                                           ` [PATCH] task_work_run: don't take ->pi_lock unconditionally Oleg Nesterov
2020-02-20 16:39                                             ` Peter Zijlstra
2020-02-20 17:22                                               ` Oleg Nesterov
2020-02-20 17:49                                                 ` Peter Zijlstra
2020-02-21 14:52                                                   ` Oleg Nesterov
2020-02-18 16:46                                       ` [ISSUE] The time cost of IOSQE_IO_LINK Jens Axboe
2020-02-18 16:52                                         ` Jens Axboe
2020-02-18 13:13                               ` Peter Zijlstra

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