| Message ID | 1353934099-18685-2-git-send-email-ville.syrjala@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, 26 Nov 2012 14:48:18 +0200, ville.syrjala@linux.intel.com wrote: > From: Ville Syrjälä <ville.syrjala@linux.intel.com> > > According to BSpec the ring head and tail pointers must not be > on the same cacheline when head > tail. The easiest way to enforce > this is to reduce the reported ring space. I'm going to admit blindness because I don't see that warning in the gen2-gen7 bspecs. Can you please give chapter and verse, and check to see if there is a rationale? -Chris
On Mon, Nov 26, 2012 at 04:28:33PM +0000, Chris Wilson wrote: > On Mon, 26 Nov 2012 14:48:18 +0200, ville.syrjala@linux.intel.com wrote: > > From: Ville Syrjälä <ville.syrjala@linux.intel.com> > > > > According to BSpec the ring head and tail pointers must not be > > on the same cacheline when head > tail. The easiest way to enforce > > this is to reduce the reported ring space. > > I'm going to admit blindness because I don't see that warning in the > gen2-gen7 bspecs. Can you please give chapter and verse, and check to > see if there is a rationale? It's always the last thing in the section titled 'Ring Buffer Use'. I believe it's present in all the pre-snb internal bspecs, and it's also in all the public docs. I can't find it in the internal snb+ bspec but then again those don't seem to include the relevant chapter at all. Of course I can't be sure if it's a valid issue, or just something that got faithfully copypasted from one document to the next.
diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c index 2cba7b4..d184727 100644 --- a/drivers/gpu/drm/i915/i915_dma.c +++ b/drivers/gpu/drm/i915/i915_dma.c @@ -168,7 +168,7 @@ void i915_kernel_lost_context(struct drm_device * dev) ring->head = I915_READ_HEAD(ring) & HEAD_ADDR; ring->tail = I915_READ_TAIL(ring) & TAIL_ADDR; - ring->space = ring->head - (ring->tail + 8); + ring->space = ring->head - (ring->tail + 64); if (ring->space < 0) ring->space += ring->size; diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c index c828169..70a184e 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -46,7 +46,7 @@ struct pipe_control { static inline int ring_space(struct intel_ring_buffer *ring) { - int space = (ring->head & HEAD_ADDR) - (ring->tail + 8); + int space = (ring->head & HEAD_ADDR) - (ring->tail + 64); if (space < 0) space += ring->size; return space; @@ -1163,7 +1163,7 @@ static int intel_ring_wait_request(struct intel_ring_buffer *ring, int n) if (request->tail == -1) continue; - space = request->tail - (ring->tail + 8); + space = request->tail - (ring->tail + 64); if (space < 0) space += ring->size; if (space >= n) { diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h index 2ea7a31..b15f896 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.h +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h @@ -187,7 +187,7 @@ void intel_cleanup_ring_buffer(struct intel_ring_buffer *ring); int __must_check intel_wait_ring_buffer(struct intel_ring_buffer *ring, int n); static inline int intel_wait_ring_idle(struct intel_ring_buffer *ring) { - return intel_wait_ring_buffer(ring, ring->size - 8); + return intel_wait_ring_buffer(ring, ring->size - 64); } int __must_check intel_ring_begin(struct intel_ring_buffer *ring, int n);