On Tue, May 24, 2016 at 10:27:19AM +0200, Daniel Vetter wrote: > On Mon, May 23, 2016 at 05:09:43PM +0300, [email protected] wrote: > > From: Ville Syrjälä <[email protected]> > > > > On SNB (at least) it's dangeruopus to hang the GPU with an infinite > > batch buffer loop while RPS is disabled. The only thing that keeps > > the system going in such circumstances are the internal RPS timers, > > so we should never feed the GPU with RPS disabled unless we want to > > risk a total system hang. > > > > Previously we didn't fully disable RPS, but that changes in > > commit 2030d684f7b3 ("drm/i915/bxt: Explicitly clear the Turbo control > > register") > > so we probably didn't see the problem so often previously. But > > even before that we were at the mercy of the BIOS for the initial > > RPS state, so if the BIOS didn't enable RPS a GPU hang immediately > > upon boot could have been fatal. > > > > To avoid the problems let's just make the RPS enable immediate. > > This renders the delayed_resume_work useless actually. We could perhaps > > just move the ring freq table initialization to the work and do the > > other stull synchronously? > > > > Fixes: 2030d684f7b3 ("drm/i915/bxt: Explicitly clear the Turbo control > > register") > > Signed-off-by: Ville Syrjälä <[email protected]> > > --- > > This is more and RFC at this point. Perhaps we might want to keep the > > delayed > > work but just for the ring freq table update (which is the main reson this > > whole > > thing exists in the first place). Another factor is that wait_for() is not > > exactly optiomal currently, so it makes the operation slower than it needs > > to > > be. Would need some hard numbers to see if it's worth keeping the delayed > > work > > or not I suppose. > > Loading the ring freq tables takes forever, so definitely want to keep > that.
It only takes forever becasue wait_for() sucks. with current sleep duration of 1000-2000 us: [ 308.231364] rps init took 5533 us [ 308.266322] ring freq init took 34952 us sleep duration reduced to 100-200 us: [ 155.367588] rps init took 679 us [ 155.371100] ring freq init took 3509 us So looks like someone just failed to root cause the slowness, and then went on to optimize the wrong thing. > I'd just split rps setup in two parts and push the schedule_work > down a bit. Long term we can go overboard with async (and maybey only > stall for all the GT setup in the very first batchbuffer). > -Daniel > > > > > drivers/gpu/drm/i915/intel_pm.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/drivers/gpu/drm/i915/intel_pm.c > > b/drivers/gpu/drm/i915/intel_pm.c > > index 817c84c22782..e65c5c2b9b4e 100644 > > --- a/drivers/gpu/drm/i915/intel_pm.c > > +++ b/drivers/gpu/drm/i915/intel_pm.c > > @@ -6505,6 +6505,7 @@ void intel_enable_gt_powersave(struct > > drm_i915_private *dev_priv) > > if (schedule_delayed_work(&dev_priv->rps.delayed_resume_work, > > round_jiffies_up_relative(HZ))) > > intel_runtime_pm_get_noresume(dev_priv); > > + flush_delayed_work(&dev_priv->rps.delayed_resume_work); > > } > > } > > > > -- > > 2.7.4 > > > > _______________________________________________ > > Intel-gfx mailing list > > [email protected] > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx > > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch -- Ville Syrjälä Intel OTC _______________________________________________ Intel-gfx mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/intel-gfx
