[Intel-gfx] [PATCH] drm/i915: Wait for completion of pending flips when starved of fences

[Chris Wilson]

On Mon, Jan 20, 2014 at 11:37:42AM +0100, Daniel Vetter wrote:
> On Mon, Jan 20, 2014 at 09:49:24AM +0000, Chris Wilson wrote:
> > On Sun, Jan 19, 2014 at 10:55:26PM +0100, Daniel Vetter wrote:
> > > Also there's a certain chance we'll starve
> > > the unpin work, similar to the issues around flushing the unpin work
> > > in our pageflip implementation.
> > 
> > If you mean that we will never run the unpin workqueue, that's what the
> > implementation will fix, eventually, after a busy-spin in userspace since
> > set_need_resched() was removed. I can teach userspace to yield() after
> > an EAGAIN which seems a reasonable compromise (userspace gets a bonus
> > for being cooperative rather than penalized for using up its timeslice.)
> 
> yield won't help, we need to block on the work-queue draining like we do
> in the pageflip code with flush_workqueue. At least we've had bug reports
> in the past where someone found it intriguing to run his entire userspace
> with rt prio, which ended up starving the sched_normal workqueue and so
> livelocked the entire system.

But isn't that exactly the behaviour the RT user programmed?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre