[Mesa-dev] [PATCH v2 24/37] panfrost: Cache GPU accesses to BOs

[Boris Brezillon]

This way we can avoid calling ioctl(WAIT_BO) when we already know the
BO is idle because it hasn't been touched by a GPU job or because the
previous call to panfrost_bo_wait() returned true.

Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
---
 src/gallium/drivers/panfrost/pan_bo.c  | 40 +++++++++++++++++++++++---
 src/gallium/drivers/panfrost/pan_bo.h  |  9 +++++-
 src/gallium/drivers/panfrost/pan_job.c |  7 +++++
 3 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/src/gallium/drivers/panfrost/pan_bo.c b/src/gallium/drivers/panfrost/pan_bo.c
index 4aabd5fd23ab..c3b62c369f3e 100644
--- a/src/gallium/drivers/panfrost/pan_bo.c
+++ b/src/gallium/drivers/panfrost/pan_bo.c
@@ -102,9 +102,18 @@ panfrost_bo_free(struct panfrost_bo *bo)
         ralloc_free(bo);
 }
 
-/* Returns true if the BO is ready, false otherwise. */
+/* Returns true if the BO is ready, false otherwise.
+ * access_type is encoding the type of access one wants to ensure is done.
+ * Say you want to make sure all writers are done writing, you should pass
+ * PAN_BO_GPU_ACCESS_WRITE.
+ * If you want to wait for all users, you should pass PAN_BO_GPU_ACCESS_RW.
+ * PAN_BO_GPU_ACCESS_READ would work too as waiting for readers implies
+ * waiting for writers as well, but we want to make things explicit and waiting
+ * only for readers is impossible.
+ */
 bool
-panfrost_bo_wait(struct panfrost_bo *bo, int64_t timeout_ns)
+panfrost_bo_wait(struct panfrost_bo *bo, int64_t timeout_ns,
+                 uint32_t access_type)
 {
         struct drm_panfrost_wait_bo req = {
                 .handle = bo->gem_handle,
@@ -112,12 +121,34 @@ panfrost_bo_wait(struct panfrost_bo *bo, int64_t timeout_ns)
         };
         int ret;
 
+        assert(access_type == PAN_BO_GPU_ACCESS_WRITE ||
+               access_type == PAN_BO_GPU_ACCESS_RW);
+
+        /* If the BO has been exported or imported we can't rely on the cached
+         * state, we need to call the WAIT_BO ioctl.
+         */
+        if (!(bo->flags & (PAN_BO_IMPORTED | PAN_BO_EXPORTED))) {
+                /* If ->gpu_access is 0, the BO is idle, and if the WRITE flag
+                 * is cleared, that means we only have readers.
+                 */
+                if (!bo->gpu_access)
+                        return true;
+                else if (!(access_type & PAN_BO_GPU_ACCESS_READ) &&
+                         !(bo->gpu_access & PAN_BO_GPU_ACCESS_WRITE))
+                        return true;
+        }
+
         /* The ioctl returns >= 0 value when the BO we are waiting for is ready
          * -1 otherwise.
          */
         ret = drmIoctl(bo->screen->fd, DRM_IOCTL_PANFROST_WAIT_BO, &req);
-        if (ret != -1)
+        if (ret != -1) {
+                /* Set gpu_access to 0 so that the next call to bo_wait()
+                 * doesn't have to call the WAIT_BO ioctl.
+                 */
+                bo->gpu_access = 0;
                 return true;
+        }
 
         /* If errno is not ETIMEDOUT or EBUSY that means the handle we passed
          * is invalid, which shouldn't happen here.
@@ -174,7 +205,8 @@ panfrost_bo_cache_fetch(struct panfrost_screen *screen,
                 if (entry->size < size || entry->flags != flags)
                         continue;
 
-                if (!panfrost_bo_wait(entry, dontwait ? 0 : INT64_MAX))
+                if (!panfrost_bo_wait(entry, dontwait ? 0 : INT64_MAX,
+                                      PAN_BO_GPU_ACCESS_RW))
                         continue;
 
                 struct drm_panfrost_madvise madv = {
diff --git a/src/gallium/drivers/panfrost/pan_bo.h b/src/gallium/drivers/panfrost/pan_bo.h
index a4b4d05b96e9..60ccb0c075a6 100644
--- a/src/gallium/drivers/panfrost/pan_bo.h
+++ b/src/gallium/drivers/panfrost/pan_bo.h
@@ -100,10 +100,17 @@ struct panfrost_bo {
         int gem_handle;
 
         uint32_t flags;
+
+        /* Combination of PAN_BO_GPU_ACCESS_{READ,WRITE} flags encoding pending
+         * GPU accesses to this BO. Useful to avoid calling the WAIT_BO ioctl
+         * when the BO is idle.
+         */
+        uint32_t gpu_access;
 };
 
 bool
-panfrost_bo_wait(struct panfrost_bo *bo, int64_t timeout_ns);
+panfrost_bo_wait(struct panfrost_bo *bo, int64_t timeout_ns,
+                 uint32_t access_type);
 void
 panfrost_bo_reference(struct panfrost_bo *bo);
 void
diff --git a/src/gallium/drivers/panfrost/pan_job.c b/src/gallium/drivers/panfrost/pan_job.c
index 739f36a593f1..30720ab98bb9 100644
--- a/src/gallium/drivers/panfrost/pan_job.c
+++ b/src/gallium/drivers/panfrost/pan_job.c
@@ -389,8 +389,15 @@ panfrost_batch_submit_ioctl(struct panfrost_batch *batch,
 
         hash_table_foreach(batch->bos, entry) {
                 struct panfrost_bo *bo = (struct panfrost_bo *)entry->key;
+                uint32_t flags = (uintptr_t)entry->data;
+
                 assert(bo->gem_handle > 0);
                 bo_handles[submit.bo_handle_count++] = bo->gem_handle;
+
+                /* Update the BO access flags so that panfrost_bo_wait() knows
+                 * about all pending accesses.
+                 */
+                bo->gpu_access |= flags & (PAN_BO_GPU_ACCESS_RW);
         }
 
         submit.bo_handles = (u64) (uintptr_t) bo_handles;
-- 
2.21.0