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: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170504130846.4807-3-chris@chris-wilson.co.uk
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@ -1656,7 +1656,8 @@ static int ring_request_alloc(struct drm_i915_gem_request *request)
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return 0;
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}
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static int wait_for_space(struct drm_i915_gem_request *req, int bytes)
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static noinline int wait_for_space(struct drm_i915_gem_request *req,
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unsigned int bytes)
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{
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struct intel_ring *ring = req->ring;
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struct drm_i915_gem_request *target;
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@ -1701,52 +1702,56 @@ static int wait_for_space(struct drm_i915_gem_request *req, int bytes)
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return 0;
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}
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u32 *intel_ring_begin(struct drm_i915_gem_request *req, int num_dwords)
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u32 *intel_ring_begin(struct drm_i915_gem_request *req,
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unsigned int num_dwords)
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{
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struct intel_ring *ring = req->ring;
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int remain_actual = ring->size - ring->emit;
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int remain_usable = ring->effective_size - ring->emit;
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int bytes = num_dwords * sizeof(u32);
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int total_bytes, wait_bytes;
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bool need_wrap = false;
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const unsigned int remain_usable = ring->effective_size - ring->emit;
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const unsigned int bytes = num_dwords * sizeof(u32);
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unsigned int need_wrap = 0;
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unsigned int total_bytes;
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u32 *cs;
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total_bytes = bytes + req->reserved_space;
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GEM_BUG_ON(total_bytes > ring->effective_size);
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if (unlikely(bytes > remain_usable)) {
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/*
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* Not enough space for the basic request. So need to flush
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* out the remainder and then wait for base + reserved.
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*/
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wait_bytes = remain_actual + total_bytes;
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need_wrap = true;
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} else if (unlikely(total_bytes > remain_usable)) {
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/*
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* The base request will fit but the reserved space
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* falls off the end. So we don't need an immediate wrap
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* and only need to effectively wait for the reserved
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* size space from the start of ringbuffer.
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*/
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wait_bytes = remain_actual + req->reserved_space;
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} else {
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/* No wrapping required, just waiting. */
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wait_bytes = total_bytes;
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if (unlikely(total_bytes > remain_usable)) {
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const int remain_actual = ring->size - ring->emit;
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if (bytes > remain_usable) {
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/*
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* Not enough space for the basic request. So need to
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* flush out the remainder and then wait for
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* base + reserved.
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*/
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total_bytes += remain_actual;
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need_wrap = remain_actual | 1;
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} else {
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/*
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* The base request will fit but the reserved space
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* falls off the end. So we don't need an immediate
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* wrap and only need to effectively wait for the
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* reserved size from the start of ringbuffer.
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*/
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total_bytes = req->reserved_space + remain_actual;
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}
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}
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if (wait_bytes > ring->space) {
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int ret = wait_for_space(req, wait_bytes);
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if (unlikely(total_bytes > ring->space)) {
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int ret = wait_for_space(req, total_bytes);
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if (unlikely(ret))
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return ERR_PTR(ret);
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}
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if (unlikely(need_wrap)) {
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GEM_BUG_ON(remain_actual > ring->space);
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GEM_BUG_ON(ring->emit + remain_actual > ring->size);
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need_wrap &= ~1;
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GEM_BUG_ON(need_wrap > ring->space);
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GEM_BUG_ON(ring->emit + need_wrap > ring->size);
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/* Fill the tail with MI_NOOP */
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memset(ring->vaddr + ring->emit, 0, remain_actual);
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memset(ring->vaddr + ring->emit, 0, need_wrap);
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ring->emit = 0;
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ring->space -= remain_actual;
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ring->space -= need_wrap;
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}
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GEM_BUG_ON(ring->emit > ring->size - bytes);
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@ -497,7 +497,8 @@ void intel_legacy_submission_resume(struct drm_i915_private *dev_priv);
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int __must_check intel_ring_cacheline_align(struct drm_i915_gem_request *req);
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u32 __must_check *intel_ring_begin(struct drm_i915_gem_request *req, int n);
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u32 __must_check *intel_ring_begin(struct drm_i915_gem_request *req,
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unsigned int n);
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static inline void
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intel_ring_advance(struct drm_i915_gem_request *req, u32 *cs)
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