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From: Jens Axboe <axboe@kernel.dk>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Jann Horn <jannh@google.com>, io-uring <io-uring@vger.kernel.org>,
	Glauber Costa <glauber@scylladb.com>,
	Pavel Begunkov <asml.silence@gmail.com>
Subject: Re: [PATCH 7/9] io_uring: add per-task callback handler
Date: Fri, 21 Feb 2020 12:13:42 -0800	[thread overview]
Message-ID: <149b3b2f-0bb1-076b-0aa7-920a21a62f81@kernel.dk> (raw)
In-Reply-To: <20200221162354.GZ14897@hirez.programming.kicks-ass.net>

On 2/21/20 9:23 AM, Peter Zijlstra wrote:
> On Fri, Feb 21, 2020 at 06:49:16AM -0800, Jens Axboe wrote:
> 
>>> Jens, what exactly is the benefit of running this on every random
>>> schedule() vs in io_cqring_wait() ? Or even, since io_cqring_wait() is
>>> the very last thing the syscall does, task_work.
>>
>> I took a step back and I think we can just use the task work, which
>> makes this a lot less complicated in terms of locking and schedule
>> state. Ran some quick testing with the below and it works for me.
>>
>> I'm going to re-spin based on this and just dump the sched_work
>> addition.
> 
> Aswesome, simpler is better.

Agree!

>> @@ -5392,6 +5392,12 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
>>  						TASK_INTERRUPTIBLE);
>>  		if (io_should_wake(&iowq, false))
>>  			break;
>> +		if (current->task_works) {
>> +			task_work_run();
>> +			if (io_should_wake(&iowq, false))
>> +				break;
>> +			continue;
>> +		}
> 
> 		if (current->task_works)
> 			task_work_run();
> 		if (io_should_wake(&iowq, false);
> 			break;
> 
> doesn't work?

Yeah it totally does, I'll make that change. Not sure what I was
thinking there.

>>  		schedule();
>>  		if (signal_pending(current)) {
>>  			ret = -EINTR;
> 
> 
> Anyway, we need to be careful about the context where we call
> task_work_run(), but afaict doing it here should be fine.

Right, that's the main win over the sched in/out approach. On clean
entry to a system call we should be fine, I added it for
io_uring_enter() as well. We're not holding anything at that point.

-- 
Jens Axboe


  reply	other threads:[~2020-02-21 20:13 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-20 20:31 [PATCHSET 0/9] io_uring: use polled async retry Jens Axboe
2020-02-20 20:31 ` [PATCH 1/9] io_uring: consider any io_read/write -EAGAIN as final Jens Axboe
2020-02-20 20:31 ` [PATCH 2/9] io_uring: io_accept() should hold on to submit reference on retry Jens Axboe
2020-02-20 20:31 ` [PATCH 3/9] sched: move io-wq/workqueue worker sched in/out into helpers Jens Axboe
2020-02-20 20:31 ` [PATCH 4/9] task_work_run: don't take ->pi_lock unconditionally Jens Axboe
2020-02-20 20:31 ` [PATCH 5/9] kernel: abstract out task work helpers Jens Axboe
2020-02-20 21:07   ` Peter Zijlstra
2020-02-20 21:08     ` Jens Axboe
2020-02-20 20:31 ` [PATCH 6/9] sched: add a sched_work list Jens Axboe
2020-02-20 21:17   ` Peter Zijlstra
2020-02-20 21:53     ` Jens Axboe
2020-02-20 22:02       ` Jens Axboe
2020-02-20 20:31 ` [PATCH 7/9] io_uring: add per-task callback handler Jens Axboe
2020-02-20 22:02   ` Jann Horn
2020-02-20 22:14     ` Jens Axboe
2020-02-20 22:18       ` Jens Axboe
2020-02-20 22:25         ` Jann Horn
2020-02-20 22:23       ` Jens Axboe
2020-02-20 22:38         ` Jann Horn
2020-02-20 22:56           ` Jens Axboe
2020-02-20 22:58             ` Jann Horn
2020-02-20 23:02               ` Jens Axboe
2020-02-20 22:23       ` Jann Horn
2020-02-20 23:00         ` Jens Axboe
2020-02-20 23:12           ` Jann Horn
2020-02-20 23:22             ` Jens Axboe
2020-02-21  1:29               ` Jann Horn
2020-02-21 17:32                 ` Jens Axboe
2020-02-21 19:24                   ` Jann Horn
2020-02-21 20:18                     ` Jens Axboe
2020-02-20 22:56     ` Jann Horn
2020-02-21 10:47     ` Peter Zijlstra
2020-02-21 14:49       ` Jens Axboe
2020-02-21 15:02         ` Jann Horn
2020-02-21 16:12           ` Peter Zijlstra
2020-02-21 16:23         ` Peter Zijlstra
2020-02-21 20:13           ` Jens Axboe [this message]
2020-02-21 13:51   ` Pavel Begunkov
2020-02-21 14:50     ` Jens Axboe
2020-02-21 18:30       ` Pavel Begunkov
2020-02-21 19:10         ` Jens Axboe
2020-02-21 19:22           ` Pavel Begunkov
2020-02-23  6:00           ` Jens Axboe
2020-02-23  6:26             ` Jens Axboe
2020-02-23 11:02               ` Pavel Begunkov
2020-02-23 14:49                 ` Jens Axboe
2020-02-23 14:58                   ` Jens Axboe
2020-02-23 15:07                     ` Jens Axboe
2020-02-23 18:04                       ` Pavel Begunkov
2020-02-23 18:06                         ` Jens Axboe
2020-02-23 17:55                   ` Pavel Begunkov
2020-02-20 20:31 ` [PATCH 8/9] io_uring: mark requests that we can do poll async in io_op_defs Jens Axboe
2020-02-20 20:31 ` [PATCH 9/9] io_uring: use poll driven retry for files that support it Jens Axboe

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