[Mesa-dev] [PATCH v3] i965: Track last location of bo used for the batch

[Chris Wilson]

Borrow a trick from anv, and use the last known index for the bo to skip
a search of the batch->exec_bo when adding a new relocation. In defence
against the bo being used in multiple batches simultaneously, we check
that this slot exists and points back to us.

v2: Also update brw_batch_references()
v3: Reset bo->index on creation (Daniel)

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>
Cc: Jason Ekstrand <jason.ekstrand at intel.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 src/mesa/drivers/dri/i965/brw_bufmgr.c        |  1 +
 src/mesa/drivers/dri/i965/brw_bufmgr.h        |  7 +++++++
 src/mesa/drivers/dri/i965/intel_batchbuffer.c | 18 ++++++++++++++++--
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.c b/src/mesa/drivers/dri/i965/brw_bufmgr.c
index da12a13152..4e43a448ae 100644
--- a/src/mesa/drivers/dri/i965/brw_bufmgr.c
+++ b/src/mesa/drivers/dri/i965/brw_bufmgr.c
@@ -353,6 +353,7 @@ retry:
    p_atomic_set(&bo->refcount, 1);
    bo->reusable = true;
    bo->cache_coherent = bufmgr->has_llc;
+   bo->index = -1;
 
    pthread_mutex_unlock(&bufmgr->lock);
 
diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.h b/src/mesa/drivers/dri/i965/brw_bufmgr.h
index 4d671b6aae..27a27ca244 100644
--- a/src/mesa/drivers/dri/i965/brw_bufmgr.h
+++ b/src/mesa/drivers/dri/i965/brw_bufmgr.h
@@ -76,6 +76,13 @@ struct brw_bo {
    uint64_t offset64;
 
    /**
+    * Index of this buffer inside the batch, -1 when not in a batch. Note
+    * that a single buffer may be in multiple batches (contexts), the index
+    * only refers to its last use and should not be trusted!
+    */
+   unsigned int index;
+
+   /**
     * Boolean of whether the GPU is definitely not accessing the buffer.
     *
     * This is only valid when reusable, since non-reusable
diff --git a/src/mesa/drivers/dri/i965/intel_batchbuffer.c b/src/mesa/drivers/dri/i965/intel_batchbuffer.c
index 62d2fe8ef3..f76ece8d71 100644
--- a/src/mesa/drivers/dri/i965/intel_batchbuffer.c
+++ b/src/mesa/drivers/dri/i965/intel_batchbuffer.c
@@ -515,12 +515,20 @@ throttle(struct brw_context *brw)
    }
 }
 
+#define READ_ONCE(x) (*(volatile __typeof__(x) *)&(x))
+
 static void
 add_exec_bo(struct intel_batchbuffer *batch, struct brw_bo *bo)
 {
    if (bo != batch->bo) {
-      for (int i = 0; i < batch->exec_count; i++) {
-         if (batch->exec_bos[i] == bo)
+      unsigned int index = READ_ONCE(bo->index);
+
+      if (index < batch->exec_count && batch->exec_bos[index] == bo)
+         return;
+
+      /* May have been shared between multiple active batches */
+      for (index = 0; index < batch->exec_count; index++) {
+         if (batch->exec_bos[index] == bo)
             return;
       }
 
@@ -553,6 +561,7 @@ add_exec_bo(struct intel_batchbuffer *batch, struct brw_bo *bo)
    validation_entry->rsvd1 = 0;
    validation_entry->rsvd2 = 0;
 
+   bo->index = batch->exec_count;
    batch->exec_bos[batch->exec_count] = bo;
    batch->exec_count++;
    batch->aperture_space += bo->size;
@@ -597,6 +606,7 @@ execbuffer(int fd,
       struct brw_bo *bo = batch->exec_bos[i];
 
       bo->idle = false;
+      bo->index = -1;
 
       /* Update brw_bo::offset64 */
       if (batch->exec_objects[i].offset != bo->offset64) {
@@ -742,6 +752,10 @@ brw_batch_has_aperture_space(struct brw_context *brw, unsigned extra_space)
 bool
 brw_batch_references(struct intel_batchbuffer *batch, struct brw_bo *bo)
 {
+   unsigned int index = READ_ONCE(bo->index);
+   if (index < batch->exec_count && batch->exec_bos[index] == bo)
+      return true;
+
    for (int i = 0; i < batch->exec_count; i++) {
       if (batch->exec_bos[i] == bo)
          return true;
-- 
2.13.2