Re: [PATCH] io_uring: get rid of intermediate aux cqe caches

[Pavel Begunkov <asml.silence@gmail.com>]

On 3/4/24 22:07, Pavel Begunkov wrote:
> On 3/1/24 03:45, Jens Axboe wrote:
>> On 2/29/24 9:36 AM, Pavel Begunkov wrote:
>>> With defer taskrun we store aux cqes into a cache array and then flush
>>> into the CQ, and we also maintain the ordering so aux cqes are flushed
>>> before request completions. Why do we need the cache instead of pushing
>>> them directly? We acutally don't, so let's kill it.
>>>
>>> One nuance is synchronisation -- the path we touch here is only for
>>> DEFER_TASKRUN and guaranteed to be executed in the task context, and
>>> all cqe posting is serialised by that. We also don't need locks because
>>> of that, see __io_cq_lock().
>>
>> Nicely spotted! Looks good to me.
> 
> Apparently I'm wrong as "defer" in that function is not about
> defer taskrun, but rather IO_URING_F_COMPLETE_DEFER. Jens, can
> you drop it for now?

One way forward would be to limit the aux fast path to defer
taskrun, I don't really care about other cases, and aux is
mostly useful for multishots hence net, which should preferably
be DEFER_TASKRUN.

In any case the code is a bit unhandy if not smelly, can use
some refactoring.

-- 
Pavel Begunkov