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From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 0/2] Optimise io_uring completion waiting
Date: Sat, 14 Sep 2019 13:11:08 +0300
Message-ID: <cb105638-2394-5eef-216f-9c6ff918ee59@gmail.com> (raw)
In-Reply-To: <af5ba045-2ea8-b213-3625-354c10334540@kernel.dk>

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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@gmail.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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      reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-13 22:28 Pavel Begunkov (Silence)
2019-09-13 22:28 ` [RFC PATCH 1/2] sched/wait: Add wait_threshold Pavel Begunkov (Silence)
2019-09-13 22:28 ` [RFC PATCH 2/2] io_uring: Optimise cq waiting with wait_threshold Pavel Begunkov (Silence)
2019-09-14  0:31 ` [RFC PATCH 0/2] Optimise io_uring completion waiting Jens Axboe
2019-09-14 10:11   ` Pavel Begunkov [this message]

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