> -----Original Message----- > From: Intel-gfx [mailto:intel-gfx-bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of > John.C.Harrison@xxxxxxxxx > Sent: Thursday, March 19, 2015 12:30 PM > To: Intel-GFX@xxxxxxxxxxxxxxxxxxxxx > Subject: [PATCH 04/59] drm/i915: Fix for ringbuf space wait in LRC > mode > > From: John Harrison <John.C.Harrison@xxxxxxxxx> > > The legacy and LRC code paths have an almost identical procedure for waiting > for > space in the ring buffer. They both search for a request in the free list that > will advance the tail to a point where sufficient space is available. They then > wait for that request, retire it and recalculate the free space value. > > Unfortunately, a bug in the LRC side meant that the resulting free space might > not be as large as expected and indeed, might not be sufficient. This is because > it was testing against the value of request->tail not request->postfix. Whereas, > when a request is retired, ringbuf->tail is updated to req->postfix not > req->tail. > > Another significant difference between the two is that the LRC one did not trust > the wait for request to work! It redid the is there enough space available test > and would fail the call if insufficient. Whereas, the legacy version just said > 'return 0' - it assumed the preceeding code works. This difference meant that > the LRC version still worked even with the bug - it just fell back to the > polling wait path. > > For: VIZ-5115 > Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_lrc.c | 10 ++++++---- > drivers/gpu/drm/i915/intel_ringbuffer.c | 10 ++++++---- > 2 files changed, 12 insertions(+), 8 deletions(-) > > diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c > index 6504689..1c3834fc 100644 > --- a/drivers/gpu/drm/i915/intel_lrc.c > +++ b/drivers/gpu/drm/i915/intel_lrc.c > @@ -634,7 +634,7 @@ static int logical_ring_wait_request(struct > intel_ringbuffer *ringbuf, > { > struct intel_engine_cs *ring = ringbuf->ring; > struct drm_i915_gem_request *request; > - int ret; > + int ret, new_space; > > if (intel_ring_space(ringbuf) >= bytes) > return 0; > @@ -650,10 +650,10 @@ static int logical_ring_wait_request(struct > intel_ringbuffer *ringbuf, > continue; > > /* Would completion of this request free enough space? */ > - if (__intel_ring_space(request->tail, ringbuf->tail, > - ringbuf->size) >= bytes) { > + new_space = __intel_ring_space(request->postfix, ringbuf->tail, > + ringbuf->size); > + if (new_space >= bytes) > break; > - } > } > > if (&request->list == &ring->request_list) > @@ -665,6 +665,8 @@ static int logical_ring_wait_request(struct > intel_ringbuffer *ringbuf, > > i915_gem_retire_requests_ring(ring); > > + WARN_ON(intel_ring_space(ringbuf) < new_space); > + > return intel_ring_space(ringbuf) >= bytes ? 0 : -ENOSPC; > } > > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c > b/drivers/gpu/drm/i915/intel_ringbuffer.c > index 99fb2f0..a26bdf8 100644 > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c > @@ -2059,16 +2059,16 @@ static int intel_ring_wait_request(struct > intel_engine_cs *ring, int n) > { > struct intel_ringbuffer *ringbuf = ring->buffer; > struct drm_i915_gem_request *request; > - int ret; > + int ret, new_space; > > if (intel_ring_space(ringbuf) >= n) > return 0; > > list_for_each_entry(request, &ring->request_list, list) { > - if (__intel_ring_space(request->postfix, ringbuf->tail, > - ringbuf->size) >= n) { > + new_space = __intel_ring_space(request->postfix, ringbuf->tail, > + ringbuf->size); > + if (new_space >= n) > break; > - } > } > > if (&request->list == &ring->request_list) > @@ -2080,6 +2080,8 @@ static int intel_ring_wait_request(struct > intel_engine_cs *ring, int n) > > i915_gem_retire_requests_ring(ring); > > + WARN_ON(intel_ring_space(ringbuf) < new_space); > + > return 0; > } > > -- > 1.7.9.5 Reviewed-by: Thomas Daniel <thomas.daniel@xxxxxxxxx> _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
