On Tue, Feb 24, 2015 at 01:23:27PM +0200, Mika Kuoppala wrote: > Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes: > > > On Tue, Feb 24, 2015 at 11:39:08AM +0100, Daniel Vetter wrote: > >> On Tue, Feb 24, 2015 at 08:31:18AM +0000, Chris Wilson wrote: > >> > On Tue, Feb 24, 2015 at 12:58:19AM +0100, Daniel Vetter wrote: > >> > > On Thu, Feb 19, 2015 at 04:41:12PM +0000, Chris Wilson wrote: > >> > > > On Thu, Feb 19, 2015 at 06:18:55PM +0200, Mika Kuoppala wrote: > >> > > > > There are multiple players interested in the ring->request_list > >> > > > > state. Request submission can happen in kernel or user context, > >> > > > > idle worker is going through request list to free items. And then there > >> > > > > is hangcheck worker which tries to figure out if particular ring is > >> > > > > healthy by peeking at the request list among other things. And if > >> > > > > judged stuck by hangcheck, error state is colleted. Which in turns > >> > > > > needs access to ring->request_list. > >> > > > > >> > > > We have discussed this before. Hangcheck does not need the lock so long > >> > > > as it is serialised with deletion. List processing with hangcheck during > >> > > > concurrent addition is safe. > >> > > > > >> > > > For example, I expect the request locking to look like > >> > > > > >> > > > http://cgit.freedesktop.org/~ickle/linux-2.6/tree/drivers/gpu/drm/i915/i915_gem_request.c#n691 > >> > > > >> > > I think longer-term with per-engine reset and fun stuff like that we > >> > > probably want the spinlock, just to avoid too many headaches with locking > >> > > auditing. For the execbuf fastpath it should just be one more spinlock per > >> > > ioctl, so hopefully bearable. > >> > > >> > But it is not even the locking bug that breaks capture, so what's the > >> > point? > >> > >> Oh I've read the patch as general prep work for more finegrained reset > >> support not as a fix for the referenced bug. I guess the bug is just the > >> usual incoherent seqno/irq thing that's been plagueing us ever since gen6? > > > > I presumed Mika wants to fix that hangcheck and capture may explode as > > requests are completed concurrently. The bug that I expect will remain > > is that we peek at the bo without locks during capture. > > -Chris > > > > What I think is the failure mode on [1] is: > > Request gets added to the ring but not yet > into the ring->request_list, gpu finishes it and updates > the hw status page. Hangcheck runs and sees that request_list > does not contain the supposed request and complains > that the hangcheck was activated on idle ring. > > https://bugs.freedesktop.org/show_bug.cgi?id=88651 Oh, the easiest way to prevent that was to force hangcheck to go through two passes before declaring a missed interrupt - and that there were no interrupts in the meantime. http://cgit.freedesktop.org/~ickle/linux-2.6/tree/drivers/gpu/drm/i915/i915_irq.c#n2973 -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
