drm/i915: Avoid the branch in computing intel_ring_space() (605d5b32) · Commits · 戴 / test

drivers/gpu/drm/i915/intel_ringbuffer.c

+13 −11

Original line number	Diff line number	Diff line
		@@ -39,12 +39,17 @@
		*/
		#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."
		*/
		GEM_BUG_ON(!is_power_of_2(size));
		return (head - tail - CACHELINE_BYTES) & (size - 1);
		}

		void intel_ring_update_space(struct intel_ring *ring)
		@@ -1670,12 +1675,9 @@ 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 +1746,11 @@ 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;
		}

drivers/gpu/drm/i915/intel_ringbuffer.h

+22 −14

Original line number	Diff line number	Diff line
		@@ -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

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