linux-kernel - Re: [PATCH v2 0/2] Optimise io

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Message-ID: <731b2087-7786-5374-68ff-8cba42f0cd68@kernel.dk>
Date:   Mon, 23 Sep 2019 14:48:40 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Optimise io_uring completion waiting

On 9/23/19 10:32 AM, Pavel Begunkov wrote:
> Sorry, mixed the threads.
> 
>>>
>>> I'm not sure an extension is needed for such a special interface, why not
>>> just put a ->threshold value next to the ctx->wait field and use either
>>> the regular wait_event() APIs with the proper condition, or
>>> wait_event_cmd() style APIs if you absolutely need something more complex
>>> to happen inside?
> Ingo,
> io_uring works well without this patch just using wait_event_*() with
> proper condition, but there are performance issues with spurious
> wakeups. Detailed description in the previous mail.
> Am I missing something?

I think we can do the same thing, just wrapping the waitqueue in a
structure with a count in it, on the stack. Got some flight time
coming up later today, let me try and cook up a patch.

-- 
Jens Axboe