On 2/21/20 9:23 AM, Peter Zijlstra wrote:
> On Fri, Feb 21, 2020 at 06:49:16AM -0800, Jens Axboe wrote:
>
>>> Jens, what exactly is the benefit of running this on every random
>>> schedule() vs in io_cqring_wait() ? Or even, since io_cqring_wait() is
>>> the very last thing the syscall does, task_work.
>>
>> I took a step back and I think we can just use the task work, which
>> makes this a lot less complicated in terms of locking and schedule
>> state. Ran some quick testing with the below and it works for me.
>>
>> I'm going to re-spin based on this and just dump the sched_work
>> addition.
>
> Aswesome, simpler is better.
Agree!
>> @@ -5392,6 +5392,12 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
>> TASK_INTERRUPTIBLE);
>> if (io_should_wake(&iowq, false))
>> break;
>> + if (current->task_works) {
>> + task_work_run();
>> + if (io_should_wake(&iowq, false))
>> + break;
>> + continue;
>> + }
>
> if (current->task_works)
> task_work_run();
> if (io_should_wake(&iowq, false);
> break;
>
> doesn't work?
Yeah it totally does, I'll make that change. Not sure what I was
thinking there.
>> schedule();
>> if (signal_pending(current)) {
>> ret = -EINTR;
>
>
> Anyway, we need to be careful about the context where we call
> task_work_run(), but afaict doing it here should be fine.
Right, that's the main win over the sched in/out approach. On clean
entry to a system call we should be fine, I added it for
io_uring_enter() as well. We're not holding anything at that point.
--
Jens Axboe
