| Message ID | 20180501094917.20881-1-chris@chris-wilson.co.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Quoting Chris Wilson (2018-05-01 10:49:17) > As we reschedule the requests, we do not want the submission tasklet > running until we finish updating the priority chains. (We start > rewriting priorities from the oldest, but the dequeue looks at the most > recent in-flight, so there is a small race condition where dequeue may > decide that preemption is falsely required.) Combine the tasklet kicking > from adding a new request with the set-wedge protection so that we only > have to adjust the preempt-counter once to achieve both goals. > > Reported-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> > --- > drivers/gpu/drm/i915/i915_gem.c | 4 ++-- > drivers/gpu/drm/i915/i915_request.c | 5 +---- > 2 files changed, 3 insertions(+), 6 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > index 438a2fc5bba0..a278e4dc5e09 100644 > --- a/drivers/gpu/drm/i915/i915_gem.c > +++ b/drivers/gpu/drm/i915/i915_gem.c > @@ -577,10 +577,10 @@ static void __fence_set_priority(struct dma_fence *fence, > rq = to_request(fence); > engine = rq->engine; > > - rcu_read_lock(); > + local_bh_disable(); /* 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, > diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c > index 7bb613c00cc3..eb66579db823 100644 > --- a/drivers/gpu/drm/i915/i915_request.c > +++ b/drivers/gpu/drm/i915/i915_request.c > @@ -1111,12 +1111,9 @@ void __i915_request_add(struct i915_request *request, bool flush_caches) > * decide whether to preempt the entire chain so that it is ready to > * run at the earliest possible convenience. > */ > - rcu_read_lock(); > + local_bh_disable(); > if (engine->schedule) > engine->schedule(request, &request->ctx->sched); > - rcu_read_unlock(); > - > - local_bh_disable(); > i915_sw_fence_commit(&request->submit); > local_bh_enable(); /* Kick the execlists tasklet if just scheduled */ It's an improvement in that we don't mix and match rcu/bh anymore, but it doesn't entirely close the race; as local-bh is local to this cpu and the tasklet may be running on another. Bother. -Chris
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 438a2fc5bba0..a278e4dc5e09 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -577,10 +577,10 @@ static void __fence_set_priority(struct dma_fence *fence, rq = to_request(fence); engine = rq->engine; - rcu_read_lock(); + local_bh_disable(); /* 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, diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 7bb613c00cc3..eb66579db823 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -1111,12 +1111,9 @@ void __i915_request_add(struct i915_request *request, bool flush_caches) * decide whether to preempt the entire chain so that it is ready to * run at the earliest possible convenience. */ - rcu_read_lock(); + local_bh_disable(); if (engine->schedule) engine->schedule(request, &request->ctx->sched); - rcu_read_unlock(); - - local_bh_disable(); i915_sw_fence_commit(&request->submit); local_bh_enable(); /* Kick the execlists tasklet if just scheduled */
As we reschedule the requests, we do not want the submission tasklet running until we finish updating the priority chains. (We start rewriting priorities from the oldest, but the dequeue looks at the most recent in-flight, so there is a small race condition where dequeue may decide that preemption is falsely required.) Combine the tasklet kicking from adding a new request with the set-wedge protection so that we only have to adjust the preempt-counter once to achieve both goals. Reported-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> --- drivers/gpu/drm/i915/i915_gem.c | 4 ++-- drivers/gpu/drm/i915/i915_request.c | 5 +---- 2 files changed, 3 insertions(+), 6 deletions(-)