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

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Message-ID: <cb105638-2394-5eef-216f-9c6ff918ee59@gmail.com>
Date:   Sat, 14 Sep 2019 13:11:08 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] Optimise io_uring completion waiting

It solves much of the problem, though still have overhead on traversing
a wait queue + indirect calls for checking.

I've been thinking to either
1. create n wait queues and bucketing waiter. E.g. log2(min_events)
bucketing  would remove at least half of such calls for arbitary
min_events and all if min_events is pow2.

2. or dig deeper and add custom wake_up with perhaps sorted wait_queue.
As I see it, it's pretty bulky and over-engineered, but maybe somebody
knows an easier way?

Anyway, I don't have performance numbers for that, so don't know if this
would be justified.

On 14/09/2019 03:31, Jens Axboe wrote:
> On 9/13/19 4:28 PM, Pavel Begunkov (Silence) wrote:
>> From: Pavel Begunkov <asml.silence@...il.com>
>>
>> There could be a lot of overhead within generic wait_event_*() used for
>> waiting for large number of completions. The patchset removes much of
>> it by using custom wait event (wait_threshold).
>>
>> Synthetic test showed ~40% performance boost. (see patch 2)
> 
> Nifty, from an io_uring perspective, I like this a lot.
> 
> The core changes needed to support it look fine as well. I'll await
> Peter/Ingo's comments on it.
> 

-- 
Yours sincerely,
Pavel Begunkov

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