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.
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
---
drivers/gpu/drm/i915/intel_ringbuffer.c | 63 +++++++++++++++++----------------
1 file changed, 33 insertions(+), 30 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
b/drivers/gpu/drm/i915/intel_ringbuffer.c
index c46e5439d379..53123c1cfcc5 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1654,7 +1654,7 @@ 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, int bytes)
{
struct intel_ring *ring = req->ring;
struct drm_i915_gem_request *target;
@@ -1702,49 +1702,52 @@ static int wait_for_space(struct drm_i915_gem_request
*req, int bytes)
u32 *intel_ring_begin(struct drm_i915_gem_request *req, 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)) {
- /*
- * 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)) {
- /*
- * 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.
- */
- wait_bytes = remain_actual + req->reserved_space;
- } else {
- /* No wrapping required, just waiting. */
- wait_bytes = total_bytes;
+ 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.
+ */
+ 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 from the start of ringbuffer.
+ */
+ 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);
--
2.11.0
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