Re: [PATCH RFC} io_uring: io_kiocb alloc cache

Pavel Begunkov
2020-05-14T16:26:56Z

On 14/05/2020 19:18, 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.

I know how to do it right for my version.
Is it still just for fun thing, or you think it'll be useful for real I/O?

>
> 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