[Mesa-dev] [PATCH 2/9] i965: Check last known busy status on bo before asking the kernel

[Chris Wilson]

If we know the bo is idle (that is we have no submitted a command buffer
referencing this bo since the last query) we can skip asking the kernel.
Note this may report a false negative if the target is being shared
between processes (exported via dmabuf or flink). To allow the caller
control over using the last known flag, the query is split into two.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Kenneth Graunke <kenneth at whitecape.org>
Cc: Matt Turner <mattst88 at gmail.com>
---
 src/mesa/drivers/dri/i965/brw_bufmgr.c | 17 +++++------------
 src/mesa/drivers/dri/i965/brw_bufmgr.h | 33 ++++++++++++++++++++++++++++++---
 2 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.c b/src/mesa/drivers/dri/i965/brw_bufmgr.c
index 67c15878d0..01590a0b0a 100644
--- a/src/mesa/drivers/dri/i965/brw_bufmgr.c
+++ b/src/mesa/drivers/dri/i965/brw_bufmgr.c
@@ -194,21 +194,14 @@ brw_bo_reference(struct brw_bo *bo)
 }
 
 int
-brw_bo_busy(struct brw_bo *bo)
+__brw_bo_busy(struct brw_bo *bo)
 {
-   struct brw_bufmgr *bufmgr = bo->bufmgr;
-   struct drm_i915_gem_busy busy;
-   int ret;
+   struct drm_i915_gem_busy busy = { bo->gem_handle };
 
-   memclear(busy);
-   busy.handle = bo->gem_handle;
+   drmIoctl(bo->bufmgr->fd, DRM_IOCTL_I915_GEM_BUSY, &busy);
 
-   ret = drmIoctl(bufmgr->fd, DRM_IOCTL_I915_GEM_BUSY, &busy);
-   if (ret == 0) {
-      bo->idle = !busy.busy;
-      return busy.busy;
-   }
-   return false;
+   bo->idle = !busy.busy;
+   return busy.busy;
 }
 
 int
diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.h b/src/mesa/drivers/dri/i965/brw_bufmgr.h
index 70cc2bbc6c..3a397be695 100644
--- a/src/mesa/drivers/dri/i965/brw_bufmgr.h
+++ b/src/mesa/drivers/dri/i965/brw_bufmgr.h
@@ -240,11 +240,38 @@ int brw_bo_get_tiling(struct brw_bo *bo, uint32_t *tiling_mode,
  */
 int brw_bo_flink(struct brw_bo *bo, uint32_t *name);
 
+int __brw_bo_busy(struct brw_bo *bo);
+
 /**
- * Returns 1 if mapping the buffer for write could cause the process
- * to block, due to the object being active in the GPU.
+ * Returns 0 if mapping the buffer is not in active use by the gpu.
+ * If non-zero, any mapping for for write could cause the process
+ * to block, due to the object being active in the GPU. If the lower
+ * 16 bits are zero, then we can map for read without stalling.
+ *
+ * The last-known busy status of the brw_bo is checked first. This may be
+ * stale if the brw_bo has been exported to a foriegn process. If used on an
+ * exported bo, call __brw_bo_busy() directly to bypass the local check.
  */
-int brw_bo_busy(struct brw_bo *bo);
+static inline int brw_bo_busy(struct brw_bo *bo)
+{
+   if (bo->idle) /* Note this may be stale if the bo is exported */
+      return 0;
+
+   return __brw_bo_busy(bo);
+}
+
+/**
+ * Returns true if mapping the buffer for read will cause the process to
+ * block (i.e. the buffer is still being writen). Note that when it
+ * returns false, the buffer may still be concurrently read by the GPU.
+ */
+static inline int brw_bo_write_busy(struct brw_bo *bo)
+{
+   if (bo->idle) /* Note this may be stale if the bo is exported */
+      return 0;
+
+   return __brw_bo_busy(bo) & 0xffff;
+}
 
 /**
  * Specify the volatility of the buffer.
-- 
2.11.0