Exploit the power-of-two ring size to compute the space across the wraparound using a mask rather than a if. Convert to unsigned integers so the operation is well defined.
References: https://bugs.freedesktop.org/show_bug.cgi?id=99671 Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuopp...@intel.com> Reviewed-by: Mika Kuoppala <mika.kuopp...@intel.com> --- drivers/gpu/drm/i915/intel_ringbuffer.c | 23 +++++++++++---------- drivers/gpu/drm/i915/intel_ringbuffer.h | 36 ++++++++++++++++++++------------- 2 files changed, 34 insertions(+), 25 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c index 3ce1c87dec46..e7ef04cc071b 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -39,12 +39,16 @@ */ #define LEGACY_REQUEST_SIZE 200 -static int __intel_ring_space(int head, int tail, int size) +static unsigned int __intel_ring_space(unsigned int head, + unsigned int tail, + unsigned int size) { - int space = head - tail; - if (space <= 0) - space += size; - return space - I915_RING_FREE_SPACE; + /* + * "If the Ring Buffer Head Pointer and the Tail Pointer are on the + * same cacheline, the Head Pointer must not be greater than the Tail + * Pointer." + */ + return (head - tail - CACHELINE_BYTES) & (size - 1); } void intel_ring_update_space(struct intel_ring *ring) @@ -1670,12 +1674,9 @@ static int wait_for_space(struct drm_i915_gem_request *req, int bytes) GEM_BUG_ON(!req->reserved_space); list_for_each_entry(target, &ring->request_list, ring_link) { - unsigned space; - /* Would completion of this request free enough space? */ - space = __intel_ring_space(target->postfix, ring->emit, - ring->size); - if (space >= bytes) + if (bytes <= __intel_ring_space(target->postfix, + ring->emit, ring->size)) break; } @@ -1744,11 +1745,11 @@ u32 *intel_ring_begin(struct drm_i915_gem_request *req, int num_dwords) } GEM_BUG_ON(ring->emit > ring->size - bytes); + GEM_BUG_ON(ring->space < bytes); cs = ring->vaddr + ring->emit; GEM_DEBUG_EXEC(memset(cs, POISON_INUSE, bytes)); ring->emit += bytes; ring->space -= bytes; - GEM_BUG_ON(ring->space < 0); return cs; } diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h index 600713b29d79..650ab884d6c8 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.h +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h @@ -17,17 +17,6 @@ #define CACHELINE_BYTES 64 #define CACHELINE_DWORDS (CACHELINE_BYTES / sizeof(uint32_t)) -/* - * Gen2 BSpec "1. Programming Environment" / 1.4.4.6 "Ring Buffer Use" - * Gen3 BSpec "vol1c Memory Interface Functions" / 2.3.4.5 "Ring Buffer Use" - * Gen4+ BSpec "vol1c Memory Interface and Command Stream" / 5.3.4.5 "Ring Buffer Use" - * - * "If the Ring Buffer Head Pointer and the Tail Pointer are on the same - * cacheline, the Head Pointer must not be greater than the Tail - * Pointer." - */ -#define I915_RING_FREE_SPACE 64 - struct intel_hw_status_page { struct i915_vma *vma; u32 *page_addr; @@ -145,9 +134,9 @@ struct intel_ring { u32 tail; u32 emit; - int space; - int size; - int effective_size; + u32 space; + u32 size; + u32 effective_size; }; struct i915_gem_context; @@ -548,6 +537,25 @@ assert_ring_tail_valid(const struct intel_ring *ring, unsigned int tail) */ GEM_BUG_ON(!IS_ALIGNED(tail, 8)); GEM_BUG_ON(tail >= ring->size); + + /* + * "Ring Buffer Use" + * Gen2 BSpec "1. Programming Environment" / 1.4.4.6 + * Gen3 BSpec "1c Memory Interface Functions" / 2.3.4.5 + * Gen4+ BSpec "1c Memory Interface and Command Stream" / 5.3.4.5 + * "If the Ring Buffer Head Pointer and the Tail Pointer are on the + * same cacheline, the Head Pointer must not be greater than the Tail + * Pointer." + * + * We use ring->head as the last known location of the actual RING_HEAD, + * it may have advanced but in the worst case it is equally the same + * as ring->head and so we should never program RING_TAIL to advance + * into the same cacheline as ring->head. + */ +#define cacheline(a) round_down(a, CACHELINE_BYTES) + GEM_BUG_ON(cacheline(tail) == cacheline(ring->head) && + tail < ring->head); +#undef cacheline } static inline unsigned int -- 2.11.0 _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
