Re: [PATCH 2/2] io_uring: use TWA_SIGNAL for task_work if the task isn't running

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Aug 10, 2020 at 02:25:48PM -0600, Jens Axboe wrote:
> On 8/10/20 2:13 PM, Jens Axboe wrote:
> >> Would it be clearer to write it like so perhaps?
> >>
> >> 	/*
> >> 	 * Optimization; when the task is RUNNING we can do with a
> >> 	 * cheaper TWA_RESUME notification because,... <reason goes
> >> 	 * here>. Otherwise do the more expensive, but always correct
> >> 	 * TWA_SIGNAL.
> >> 	 */
> >> 	if (READ_ONCE(tsk->state) == TASK_RUNNING) {
> >> 		__task_work_notify(tsk, TWA_RESUME);
> >> 		if (READ_ONCE(tsk->state) == TASK_RUNNING)
> >> 			return;
> >> 	}
> >> 	__task_work_notify(tsk, TWA_SIGNAL);
> >> 	wake_up_process(tsk);
> > 
> > Yeah that is easier to read, wasn't a huge fan of the loop since it's
> > only a single retry kind of condition. I'll adopt this suggestion,
> > thanks!
> 
> Re-write it a bit on top of that, just turning it into two separate
> READ_ONCE, and added appropriate comments. For the SQPOLL case, the
> wake_up_process() is enough, so we can clean up that if/else.
> 
> https://git.kernel.dk/cgit/linux-block/commit/?h=io_uring-5.9&id=49bc5c16483945982cf81b0109d7da7cd9ee55ed

OK, that works for me, thanks!

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>