Quoting Tvrtko Ursulin (2018-03-23 09:46:49)
>
> On 22/03/2018 17:44, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2018-03-22 17:24:16)
> >> + itv.it_value.tv_usec = us % 1000000;
> >> + setitimer(ITIMER_REAL, &itv, NULL);
> >
> > Ok, that gives a single shot signal.
> >
> > I would have used
> > struct sigevent sev = {
> > .sigev_notify = SIGEV_THREAD,
> > .sigev_value.sigval_int = debugfs_dir
> > .sigev_notify_function = hang_handler
> > };
> > timer_create(CLOCK_MONOTONIC, &sec, &timer);
> > timer_settime(timer, 0, &its, NULL);
> >
> > Then
> >
> > static void hang_handler(union sigval arg)
> > {
> > igt_sysfs_set(arg.sival_int, "i915_wedged", 1);
> > }
> >
> > No signals, nor globals required :)
>
> I wasn't familiar with this facility.
>
> It creates a new thread, so any hopes for small microsecond delays might
> be ruined. I can try it if you think it is still worth it?
Yes, still worth a shot. We can always poke glibc for some smarts. Or
chase it ourselves with custom threading. We need an igt_debug() to
actually tell us how long it took to respond (from spin start to
gem_wait return).
> > The problem with using a signal is that it interrupts the gem_wait()
> > and so we don't actually check that it is being woken by the hang
> > because it is already awake. Gah.
>
> Hm... if I am following correctly, we end up with -ERESTARTSYS and the
> the ioctl can get restarted for us, if I would set SA_RESTART.
>
> At the moment it happens to work because drmIoctl restart the signal.
Yes. But even automatic -ERESTARTSYS handling still implies we break
i915_request_wait() due to signal_pending_state().
> >> +static void cleanup_hang(void)
> >> +{
> >> + struct itimerval itv = { };
> >> +
> >> + igt_assert_eq(setitimer(ITIMER_REAL, &itv, NULL), 0);
> >
> > You also need a sleep here as it does not flush inflight signals.
> > (Also timer_destroy :)
>
> I always pass a longer timeout to gem_wait than the signal so I think it
> should be guaranteed that the signal had fired before gem_wait will be
> exiting.
I hadn't considered that. Please leave a comment as the timer
cancellation leaving pending signals inflight is something that keeps
catching me out.
-Chris
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