Re: [PATCH for-next 4/7] io_uring: do not always run task work at the start of io_uring_enter

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

On 8/15/22 14:09, Dylan Yudaken wrote:
> It is normally better to wait for task work until after submissions. This
> will allow greater batching if either work arrives in the meanwhile, or if
> the submissions cause task work to be queued up.
> 
> For SQPOLL this also no longer runs task work, but this is handled inside
> the SQPOLL loop anyway.
> 
> For IOPOLL io_iopoll_check will run task work anyway

It's here to free resources (e.g. io_kiocb so can be reused in the
submission) and so, but we don't care much. Running them after
submission doesn't make much difference as either we go to
cq_wait, which will run it for us, or exit and again they'll be
executed.

In short, instead of moving we can just kill it.

> Signed-off-by: Dylan Yudaken <dylany@fb.com>
> ---
>   io_uring/io_uring.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 8cc4b28b1725..3b08369c3c60 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -2990,8 +2990,6 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
>   	struct fd f;
>   	long ret;
>   
> -	io_run_task_work();
> -
>   	if (unlikely(flags & ~(IORING_ENTER_GETEVENTS | IORING_ENTER_SQ_WAKEUP |
>   			       IORING_ENTER_SQ_WAIT | IORING_ENTER_EXT_ARG |
>   			       IORING_ENTER_REGISTERED_RING)))
> @@ -3060,7 +3058,11 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
>   		if ((flags & IORING_ENTER_GETEVENTS) && ctx->syscall_iopoll)
>   			goto iopoll_locked;
>   		mutex_unlock(&ctx->uring_lock);
> +		io_run_task_work();
> +	} else {
> +		io_run_task_work();
>   	}
> +
>   	if (flags & IORING_ENTER_GETEVENTS) {
>   		int ret2;
>   		if (ctx->syscall_iopoll) {

-- 
Pavel Begunkov