On 28/07/2020 15:35, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2020-07-17 14:23:22)
On 15/07/2020 12:50, Chris Wilson wrote:
Before we can execute a request, we must wait for all of its vma to be
bound. This is a frequent operation for which we can optimise away a
few atomic operations (notably a cmpxchg) in lieu of the RCU protection.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_active.h | 15 +++++++++++++++
drivers/gpu/drm/i915/i915_vma.c | 9 +++++++--
2 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
index b9e0394e2975..fb165d3f01cf 100644
--- a/drivers/gpu/drm/i915/i915_active.h
+++ b/drivers/gpu/drm/i915/i915_active.h
@@ -231,4 +231,19 @@ struct i915_active *i915_active_create(void);
struct i915_active *i915_active_get(struct i915_active *ref);
void i915_active_put(struct i915_active *ref);
+static inline int __i915_request_await_exclusive(struct i915_request *rq,
+ struct i915_active *active)
+{
+ struct dma_fence *fence;
+ int err = 0;
+
+ fence = i915_active_fence_get(&active->excl);
+ if (fence) {
+ err = i915_request_await_dma_fence(rq, fence);
+ dma_fence_put(fence);
+ }
+
+ return err;
+}
+
#endif /* _I915_ACTIVE_H_ */
diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index bc64f773dcdb..cd12047c7791 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -1167,6 +1167,12 @@ void i915_vma_revoke_mmap(struct i915_vma *vma)
list_del(&vma->obj->userfault_link);
}
+static int
+__i915_request_await_bind(struct i915_request *rq, struct i915_vma *vma)
+{
+ return __i915_request_await_exclusive(rq, &vma->active);
+}
+
int __i915_vma_move_to_active(struct i915_vma *vma, struct i915_request *rq)
{
int err;
@@ -1174,8 +1180,7 @@ int __i915_vma_move_to_active(struct i915_vma *vma, struct i915_request *rq)
GEM_BUG_ON(!i915_vma_is_pinned(vma));
/* Wait for the vma to be bound before we start! */
- err = i915_request_await_active(rq, &vma->active,
- I915_ACTIVE_AWAIT_EXCL);
+ err = __i915_request_await_bind(rq, vma);
if (err)
return err;
Looks like for like, apart from missing i915_active_acquire_if_busy
across the operation. Remind me please what is acquire/release
protecting against? :)
To protect the rbtree walk. So, this is the function we started with for
active_await, but when we added the option to walk the entire rbtree as
well, we pulled it all under a single acquire/release. perf suggests
that was a mistake if all we frequently want to do is grab the exclusive
fence for an await.
Ok!
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Regards,
Tvrtko
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