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From: Pavel Begunkov <>
To: Jens Axboe <>, Andres Freund <>
Subject: Re: Buffered IO async context overhead
Date: Tue, 10 Mar 2020 00:02:30 +0300
Message-ID: <> (raw)
In-Reply-To: <>

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.


> 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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