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From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org
Subject: Re: [RFC 0/9] scrap 24 bytes from io_kiocb
Date: Mon, 13 Jul 2020 11:17:46 +0300	[thread overview]
Message-ID: <7368254d-1f2c-2cc9-1198-8a666f7f8864@gmail.com> (raw)
In-Reply-To: <3b3ee104-ee6b-7147-0677-bd0eb4efe76e@kernel.dk>

On 12/07/2020 23:32, Jens Axboe wrote:
> On 7/12/20 11:34 AM, Pavel Begunkov wrote:
>> On 12/07/2020 18:59, Jens Axboe wrote:
>>> On 7/12/20 3:41 AM, Pavel Begunkov wrote:
>>>> Make io_kiocb slimmer by 24 bytes mainly by revising lists usage. The
>>>> drawback is adding extra kmalloc in draining path, but that's a slow
>>>> path, so meh. It also frees some space for the deferred completion path
>>>> if would be needed in the future, but the main idea here is to shrink it
>>>> to 3 cachelines in the end.
>>>>
>>>> I'm not happy yet with a few details, so that's not final, but it would
>>>> be lovely to hear some feedback.
>>>
>>> I think it looks pretty good, most of the changes are straight forward.
>>> Adding a completion entry that shares the submit space is a good idea,
>>> and really helps bring it together.
>>>
>>> From a quick look, the only part I'm not super crazy about is patch #3.
>>
>> Thanks!
>>
>>> I'd probably rather use a generic list name and not unionize the tw
>>> lists.
>>
>> I don't care much, but without compiler's help always have troubles
>> finding and distinguishing something as generic as "list".
> 
> To me, it's easier to verify that we're doing the right thing when they
> use the same list member. Otherwise you have to cross reference two
> different names, easier to shoot yourself in the foot that way. So I'd
> prefer just retaining it as 'list' or something generic.

If you don't have objections, I'll just leave it "inflight_entry". This
one is easy to grep.

>> BTW, I thought out how to bring it down to 3 cache lines, but that would
>> require taking io_wq_work out of io_kiocb and kmalloc'ing it on demand.
>> And there should also be a bunch of nice side effects like improving apoll.
> 
> How would this work with the current use of io_wq_work as storage for
> whatever bits we're hanging on to? I guess it could work with a prep
> series first more cleanly separating it, though I do feel like we've
> been getting closer to that already.

It's definitely not a single patch. I'm going to prepare a series for
discussion later, and then we'll see whether it worth it.


> Definitely always interested in shrinking io_kiocb, just need to keep
> an eye out for the fast(er) paths not needing two allocations (and
> frees) for a single request.

-- 
Pavel Begunkov

  parent reply	other threads:[~2020-07-13  8:19 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-12  9:41 [RFC 0/9] scrap 24 bytes from io_kiocb Pavel Begunkov
2020-07-12  9:41 ` [PATCH 1/9] io_uring: share completion list w/ per-op space Pavel Begunkov
2020-07-12  9:41 ` [PATCH 2/9] io_uring: rename ctx->poll into ctx->iopoll Pavel Begunkov
2020-07-12  9:41 ` [PATCH 3/9] io_uring: use inflight_entry list for iopolling Pavel Begunkov
2020-07-12  9:41 ` [PATCH 4/9] io_uring: use competion list for CQ overflow Pavel Begunkov
2020-07-12  9:41 ` [PATCH 5/9] io_uring: add req->timeout.list Pavel Begunkov
2020-07-12  9:41 ` [PATCH 6/9] io_uring: remove init for unused list Pavel Begunkov
2020-07-12  9:41 ` [PATCH 7/9] io_uring: kill rq->list and allocate it on demand Pavel Begunkov
2020-07-12  9:41 ` [PATCH 8/9] io_uring: remove sequence from io_kiocb Pavel Begunkov
2020-07-12  9:41 ` [PATCH 9/9] io_uring: place cflags into completion data Pavel Begunkov
2020-07-12 15:59 ` [RFC 0/9] scrap 24 bytes from io_kiocb Jens Axboe
2020-07-12 17:34   ` Pavel Begunkov
2020-07-12 20:32     ` Jens Axboe
2020-07-13  8:17       ` Pavel Begunkov
2020-07-13  8:17       ` Pavel Begunkov [this message]
2020-07-13 14:12         ` Jens Axboe
2020-07-13 20:45           ` Pavel Begunkov
2020-07-13 21:00             ` Jens Axboe

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