[Mesa-dev] [PATCH v2 07/10] i965: Use snoop bo for accessing query results on !llc

[Chris Wilson]

Ony non-llc architectures where we are primarily reading back the
results of the GPU queries, then we can improve performance by using a
cacheable mapping of the results. Unfortunately, enabling snooping makes
the writes from the GPU slower, which may adversely affect pipelined
query operations (where the results are used directly by the GPU and not
CPU).

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    | 23 +++++++++++++++++++++++
 src/mesa/drivers/dri/i965/brw_bufmgr.h    |  2 ++
 src/mesa/drivers/dri/i965/gen6_queryobj.c |  2 ++
 3 files changed, 27 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.c b/src/mesa/drivers/dri/i965/brw_bufmgr.c
index 7af3725640..98634cc4b6 100644
--- a/src/mesa/drivers/dri/i965/brw_bufmgr.c
+++ b/src/mesa/drivers/dri/i965/brw_bufmgr.c
@@ -661,6 +661,29 @@ brw_bo_unreference(struct brw_bo *bo)
    }
 }
 
+static bool
+__brw_bo_set_caching(struct brw_bo *bo, int caching)
+{
+   struct drm_i915_gem_caching arg = {
+      .handle = bo->gem_handle,
+      .caching = caching
+   };
+   return drmIoctl(bo->bufmgr->fd, DRM_IOCTL_I915_GEM_SET_CACHING, &arg) == 0;
+}
+
+void
+brw_bo_set_cache_coherent(struct brw_bo *bo)
+{
+   if (bo->cache_coherent)
+      return;
+
+   if (!__brw_bo_set_caching(bo, I915_CACHING_CACHED))
+      return;
+
+   bo->reusable = false;
+   bo->cache_coherent = true;
+}
+
 static void
 set_domain(struct brw_context *brw, const char *action,
            struct brw_bo *bo, uint32_t read_domains, uint32_t write_domain)
diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.h b/src/mesa/drivers/dri/i965/brw_bufmgr.h
index 9a0f2e4f3b..bc3bc2a60f 100644
--- a/src/mesa/drivers/dri/i965/brw_bufmgr.h
+++ b/src/mesa/drivers/dri/i965/brw_bufmgr.h
@@ -221,6 +221,8 @@ void brw_bo_unreference(struct brw_bo *bo);
 #define MAP_INTERNAL_MASK       (0xff << 24)
 #define MAP_RAW                 (0x01 << 24)
 
+void brw_bo_set_cache_coherent(struct brw_bo *bo);
+
 /**
  * Maps the buffer into userspace.
  *
diff --git a/src/mesa/drivers/dri/i965/gen6_queryobj.c b/src/mesa/drivers/dri/i965/gen6_queryobj.c
index e0a02972bd..8d6bd2c40c 100644
--- a/src/mesa/drivers/dri/i965/gen6_queryobj.c
+++ b/src/mesa/drivers/dri/i965/gen6_queryobj.c
@@ -316,6 +316,8 @@ gen6_alloc_query(struct brw_context *brw, struct brw_query_object *query)
       brw_bo_unreference(query->bo);
 
    query->bo = brw_bo_alloc(brw->bufmgr, "query results", 4096, 4096);
+   brw_bo_set_cache_coherent(query->bo);
+
    query->results = brw_bo_map(brw, query->bo,
                                MAP_READ | MAP_COHERENT | MAP_ASYNC);
 
-- 
2.11.0