linux-kernel - Re: [PATCH] io_uring: remove wait loop spurious wakeups

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Message-ID: <d035bb1b-e6f0-77db-a434-1761b0a7a142@gmail.com>
Date:   Tue, 8 Oct 2019 19:43:16 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] io_uring: remove wait loop spurious wakeups

On 08/10/2019 06:16, Jens Axboe wrote:
> On 10/7/19 5:18 PM, Pavel Begunkov (Silence) wrote:
>> From: Pavel Begunkov <asml.silence@...il.com>
>>
>> Any changes interesting to tasks waiting in io_cqring_wait() are
>> commited with io_cqring_ev_posted(). However, io_ring_drop_ctx_refs()
>> also tries to do that but with no reason, that means spurious wakeups
>> every io_free_req() and io_uring_enter().
>>
>> Just use percpu_ref_put() instead.
> 
> Looks good, this is a leftover from when the ctx teardown used
> the waitqueue as well.
> 
BTW, is there a reason for ref-counting in struct io_kiocb? I understand
the idea behind submission reference, but don't see any actual part
needing it.

Tested with another ref-counting patch and got +5-8% to
nops performance.


-- 
Yours sincerely,
Pavel Begunkov



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