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From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>,
	Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>,
	io-uring <io-uring@vger.kernel.org>
Cc: joseph qi <joseph.qi@linux.alibaba.com>,
	Jiufei Xue <jiufei.xue@linux.alibaba.com>
Subject: Re: [PATCH RFC} io_uring: io_kiocb alloc cache
Date: Thu, 14 May 2020 19:18:24 +0300	[thread overview]
Message-ID: <8ddf1d04-aa4a-ee91-72fa-59cb0081695c@gmail.com> (raw)
In-Reply-To: <b7e7eb5e-cbea-0c59-38b1-1043b5352e4d@kernel.dk>

On 14/05/2020 18:53, Jens Axboe wrote:
> On 5/14/20 9:37 AM, Pavel Begunkov wrote:
> Hmm yes good point, it should work pretty easily, barring the use cases
> that do IRQ complete. But that was also a special case with the other
> cache.
> 
>> BTW, there will be a lot of problems to make either work properly with
>> IORING_FEAT_SUBMIT_STABLE.
> 
> How so? Once the request is setup, any state should be retained there.

If a late alloc fails (e.g. in __io_queue_sqe()), you'd need to file a CQE with
an error. If there is no place in CQ, to postpone the completion it'd require an
allocated req. Of course it can be dropped, but I'd prefer to have strict
guarantees.

That's the same reason, I have a patch stashed, that grabs links from SQ
atomically (i.e. take all SQEs of a link or none).

-- 
Pavel Begunkov

  reply	other threads:[~2020-05-14 16:19 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-13 16:30 [PATCH RFC} io_uring: io_kiocb alloc cache Jens Axboe
2020-05-13 17:42 ` Jann Horn
2020-05-13 17:42   ` Jann Horn
2020-05-13 18:34   ` Jens Axboe
2020-05-13 19:20   ` Pekka Enberg
2020-05-13 20:09     ` Jens Axboe
2020-05-13 20:31       ` Pekka Enberg
2020-05-13 20:44         ` Jens Axboe
2020-05-14  8:25 ` Xiaoguang Wang
2020-05-14 14:22   ` Jens Axboe
2020-05-14 14:33     ` Jens Axboe
2020-05-14 14:53       ` Pavel Begunkov
2020-05-14 15:15         ` Jens Axboe
2020-05-14 15:37           ` Pavel Begunkov
2020-05-14 15:53             ` Jens Axboe
2020-05-14 16:18               ` Pavel Begunkov [this message]
2020-05-14 16:21                 ` Jens Axboe
2020-05-14 16:25                 ` Pavel Begunkov
2020-05-14 17:01                   ` Jens Axboe
2020-05-14 17:41                     ` Jens Axboe
2020-05-16  9:20       ` Xiaoguang Wang
2020-05-16 16:15     ` Xiaoguang Wang

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