Quoting Tvrtko Ursulin (2018-05-08 10:40:43) > > On 07/05/2018 14:57, Chris Wilson wrote: > > When called from process context tasklet_schedule() defers itself to > > ksoftirqd. From experience this may cause unacceptable latencies of over > > 200ms in executing the submission tasklet, our goal is to reprioritise > > the HW execution queue and trigger HW preemption immediately, so disable > > bh over the call to schedule and force the tasklet to run afterwards if > > scheduled. > > > > v2: Keep rcu_read_lock() around for PREEMPT_RCU > > > > Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> > > Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com> > > Cc: Mika Kuoppala <mika.kuopp...@linux.intel.com> > > --- > > drivers/gpu/drm/i915/i915_gem.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/gpu/drm/i915/i915_gem.c > > b/drivers/gpu/drm/i915/i915_gem.c > > index 5ece6ae4bdff..89bf5d67cb74 100644 > > --- a/drivers/gpu/drm/i915/i915_gem.c > > +++ b/drivers/gpu/drm/i915/i915_gem.c > > @@ -578,10 +578,12 @@ static void __fence_set_priority(struct dma_fence > > *fence, > > rq = to_request(fence); > > engine = rq->engine; > > > > - rcu_read_lock(); > > + local_bh_disable(); > > + rcu_read_lock(); /* RCU serialisation for set-wedged protection */ > > if (engine->schedule) > > engine->schedule(rq, attr); > > rcu_read_unlock(); > > + local_bh_enable(); /* kick the tasklets if queues were reprioritised > > */ > > } > > > > static void fence_set_priority(struct dma_fence *fence, > > > > Is the sequence not the wrong way around? I would expect disable > preemption, then disable softirq, order for disable, on ofc opposite for > enable.
We disable preemption (i.e. softirq) then mark ->schedule as being RCU protected; unwrap and re-enable preemption (kicking softirq tasklets). I felt it better to keep the RCU tight to ->schedule than let it wrap local_bh_enable() suggesting that the tasklets might need additional protection. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
