Commit 5e5655c3 authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915: Micro-optimise hotpath through intel_ring_begin() 



Typically, there is space available within the ring and if not we have
to wait (by definition a slow path). Rearrange the code to reduce the
number of branches and stack size for the hotpath, accomodating a slight
growth for the wait.

v2: Fix the new assert that packets are not larger than the actual ring.
v3: Make the parameters unsigned as well to make usage.

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarMika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170504130846.4807-3-chris@chris-wilson.co.uk
parent 95aebcb2

drivers/gpu/drm/i915/intel_ringbuffer.c

+36 −31
Original line number Diff line number Diff line
@@ -1656,7 +1656,8 @@ static int ring_request_alloc(struct drm_i915_gem_request *request) 
	return 0;

}



static int wait_for_space(struct drm_i915_gem_request *req, int bytes)

static noinline int wait_for_space(struct drm_i915_gem_request *req,

				   unsigned int bytes)

{

	struct intel_ring *ring = req->ring;

	struct drm_i915_gem_request *target;
@@ -1701,52 +1702,56 @@ static int wait_for_space(struct drm_i915_gem_request *req, int bytes) 
	return 0;

}



u32 *intel_ring_begin(struct drm_i915_gem_request *req, int num_dwords)

u32 *intel_ring_begin(struct drm_i915_gem_request *req,

		      unsigned int num_dwords)

{

	struct intel_ring *ring = req->ring;

	int remain_actual = ring->size - ring->emit;

	int remain_usable = ring->effective_size - ring->emit;

	int bytes = num_dwords * sizeof(u32);

	int total_bytes, wait_bytes;

	bool need_wrap = false;

	const unsigned int remain_usable = ring->effective_size - ring->emit;

	const unsigned int bytes = num_dwords * sizeof(u32);

	unsigned int need_wrap = 0;

	unsigned int total_bytes;

	u32 *cs;



	total_bytes = bytes + req->reserved_space;

	GEM_BUG_ON(total_bytes > ring->effective_size);



	if (unlikely(bytes > remain_usable)) {

	if (unlikely(total_bytes > remain_usable)) {

		const int remain_actual = ring->size - ring->emit;



		if (bytes > remain_usable) {

			/*

		 * Not enough space for the basic request. So need to flush

		 * out the remainder and then wait for base + reserved.

			 * Not enough space for the basic request. So need to

			 * flush out the remainder and then wait for

			 * base + reserved.

			 */

		wait_bytes = remain_actual + total_bytes;

		need_wrap = true;

	} else if (unlikely(total_bytes > remain_usable)) {

			total_bytes += remain_actual;

			need_wrap = remain_actual | 1;

		} else  {

			/*

			 * The base request will fit but the reserved space

		 * falls off the end. So we don't need an immediate wrap

		 * and only need to effectively wait for the reserved

		 * size space from the start of ringbuffer.

			 * falls off the end. So we don't need an immediate

			 * wrap and only need to effectively wait for the

			 * reserved size from the start of ringbuffer.

			 */

		wait_bytes = remain_actual + req->reserved_space;

	} else {

		/* No wrapping required, just waiting. */

		wait_bytes = total_bytes;

			total_bytes = req->reserved_space + remain_actual;

		}

	}



	if (wait_bytes > ring->space) {

		int ret = wait_for_space(req, wait_bytes);

	if (unlikely(total_bytes > ring->space)) {

		int ret = wait_for_space(req, total_bytes);

		if (unlikely(ret))

			return ERR_PTR(ret);

	}



	if (unlikely(need_wrap)) {

		GEM_BUG_ON(remain_actual > ring->space);

		GEM_BUG_ON(ring->emit + remain_actual > ring->size);

		need_wrap &= ~1;

		GEM_BUG_ON(need_wrap > ring->space);

		GEM_BUG_ON(ring->emit + need_wrap > ring->size);



		/* Fill the tail with MI_NOOP */

		memset(ring->vaddr + ring->emit, 0, remain_actual);

		memset(ring->vaddr + ring->emit, 0, need_wrap);

		ring->emit = 0;

		ring->space -= remain_actual;

		ring->space -= need_wrap;

	}



	GEM_BUG_ON(ring->emit > ring->size - bytes);

drivers/gpu/drm/i915/intel_ringbuffer.h

+2 −1
Original line number Diff line number Diff line
@@ -497,7 +497,8 @@ void intel_legacy_submission_resume(struct drm_i915_private *dev_priv); 


int __must_check intel_ring_cacheline_align(struct drm_i915_gem_request *req);



u32 __must_check *intel_ring_begin(struct drm_i915_gem_request *req, int n);

u32 __must_check *intel_ring_begin(struct drm_i915_gem_request *req,

				   unsigned int n);



static inline void

intel_ring_advance(struct drm_i915_gem_request *req, u32 *cs)

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