On Fri, Jan 23, 2015 at 02:44:07PM +0200, Mika Kuoppala wrote: > From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > When run as a timer, i915_hangcheck_elapsed() must adhere to all the > rules of running in a softirq context. This is advantageous to us as we > want to minimise the risk that a driver bug will prevent us from > detecting a hung GPU. However, that is irrelevant if the driver bug > prevents us from resetting and recovering. Still it is prudent not to > rely on mutexes inside the checker, but given the coarseness of > dev->struct_mutex doing so is extremely hard. > > Give in and run from a work queue, i.e. outside of softirq. > > v2: > > The conversion does have one significant change, from the use of > mod_timer to schedule_delayed_work, means that the time that we execute > the first hangcheck is fixed and not continually deferred by later work. > This has the advantage of not allowing userspace to fill the ring before > hangcheck can finally run. At the same time, it removes the ability for > the interrupt to defer the hangcheck as well. This is sensible for that > an interrupt is only for a single engine, whereas we perform hangcheck > globally, so whilst one ring may have hung, the other could be running > normally and preventing the hangcheck from firing. > > Cc: Jani Nikula <jani.nikula@xxxxxxxxx> > Cc: Daniel Vetter <dnaiel.vetter@xxxxxxxxx> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> (v2) > Signed-off-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxx> One thing special with timers is that they'll always run, and if you do a del_timer_sync from process context you can't deadlock with timer A because you hold some locks for timer B that's in front of A in the queues. With workqueues that's not the case, and it's really easy to cause deadlocks by blocking some random work item in front of the queue by accident. I think for this switch we need our own, dedicated hangcheck work queue, with it's own thread to make sure it gets run reliable. But besides that I really like this chnage. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
