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From: Jens Axboe <[email protected]>
To: Pavel Begunkov <[email protected]>,
	Xiaoguang Wang <[email protected]>,
	io-uring <[email protected]>
Cc: joseph qi <[email protected]>,
	Jiufei Xue <[email protected]>
Subject: Re: [PATCH RFC} io_uring: io_kiocb alloc cache
Date: Thu, 14 May 2020 10:21:40 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 5/14/20 10:18 AM, Pavel Begunkov wrote:
> 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).

OK, I see what you mean. Yeah there's definitely some quirkiness
associated with deferring the allocation. I'm currently just working off
the idea that we just need to fix the refcounts, using a relaxed
version for the cases where we don't have shared semantics. We basically
only need that for requests with out-of-line completions, like irq
completions or async completions.

-- 
Jens Axboe


  reply	other threads:[~2020-05-14 16:21 UTC|newest]

Thread overview: 21+ 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 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
2020-05-14 16:21                 ` Jens Axboe [this message]
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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