Re: [PATCH 0/3] tw mutex & IRQ rw completion batching

Jens Axboe
2021-08-19T15:53:48Z

On 8/18/21 5:42 AM, Pavel Begunkov wrote:
> In essence, it's about two features. The first one is implemented by
> 1-2 and saves ->uring_lock lock/unlock in a single call of
> tctx_task_work(). Should be useful for links, apolls and BPF requests
> at some moment.
>
> The second feature (3/3) is batching freeing and completing of
> IRQ-based read/write requests.
>
> Haven't got numbers yet, but just throwing it for public discussion.

I ran some numbers and it looks good to me, it's a nice boost for the
IRQ completions. It's funny how the initial move to task_work for IRQ
completions took a small hit, but there's so many optimizations that it
unlocks that it's already better than before.

I'd like to apply 1/3 for now, but it depends on both master and
for-5.15/io_uring. Hence I think it'd be better to defer that one until
after the initial batch has gone in.

For the batched locking, the principle is sound and measures out to be a
nice win. But I have a hard time getting over the passed lock state, I
do wonder if there's a cleaner way to accomplish this...

--
Jens Axboe