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From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, Andres Freund <andres@anarazel.de>
Cc: io-uring@vger.kernel.org
Subject: Re: Buffered IO async context overhead
Date: Tue, 10 Mar 2020 00:02:30 +0300
Message-ID: <e50a7340-845d-6261-b070-74bdf34aeab6@gmail.com> (raw)
In-Reply-To: <d704bbee-c50a-ab99-bed3-17a93e06ddeb@kernel.dk>

On 09/03/2020 23:41, Jens Axboe wrote:
> On 3/9/20 2:03 PM, Pavel Begunkov wrote:
>> On 24/02/2020 18:22, Jens Axboe wrote:
>> A problem here is that we actually have a 2D array of works because of linked
>> requests.
> 
> You could either skip anything with a link, or even just ignore it and
> simply re-queue a dependent link if it isn't hashed when it's done if
> grabbed in a batch.
> 
>> We can io_wqe_enqueue() dependant works, if have hashed requests, so delegating
>> it to other threads. But if the work->list is not per-core, it will hurt
>> locality. Either re-enqueue hashed ones if there is a dependant work. Need to
>> think how to do better.
> 
> If we ignore links for a second, I think we can all agree that it'd be a
> big win to do the batch.

Definitely

> 
> With links, worst case would then be something where every other link is
> hashed.
> 
> For a first patch, I'd be quite happy to just stop the batch if there's
> a link on a request. The normal case here is buffered writes, and
> that'll handle that case perfectly. Links will be no worse than before.
> Seems like a no-brainer to me.

That isn't really a problem, just pointing that there could be optimisations for
different cases.

-- 
Pavel Begunkov

  reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-14 19:50 Andres Freund
2020-02-14 20:13 ` Jens Axboe
2020-02-14 20:31   ` Andres Freund
2020-02-14 20:49     ` Jens Axboe
2020-02-24  9:35       ` Andres Freund
2020-02-24 15:22         ` Jens Axboe
2020-03-09 20:03           ` Pavel Begunkov
2020-03-09 20:41             ` Jens Axboe
2020-03-09 21:02               ` Pavel Begunkov [this message]
2020-03-09 21:29                 ` Jens Axboe

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