[Mesa-dev] [PATCH 7/9] 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    | 21 +++++++++++++++++++++
 src/mesa/drivers/dri/i965/brw_bufmgr.h    |  2 ++
 src/mesa/drivers/dri/i965/gen6_queryobj.c |  2 ++
 3 files changed, 25 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.c b/src/mesa/drivers/dri/i965/brw_bufmgr.c
index 9028b538c6..824bc55fb2 100644
--- a/src/mesa/drivers/dri/i965/brw_bufmgr.c
+++ b/src/mesa/drivers/dri/i965/brw_bufmgr.c
@@ -626,6 +626,27 @@ 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 214b75bf1a..188d6c5ee0 100644
--- a/src/mesa/drivers/dri/i965/brw_bufmgr.h
+++ b/src/mesa/drivers/dri/i965/brw_bufmgr.h
@@ -188,6 +188,8 @@ 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 18af608166..5c95a4bae9 100644
--- a/src/mesa/drivers/dri/i965/gen6_queryobj.c
+++ b/src/mesa/drivers/dri/i965/gen6_queryobj.c
@@ -316,6 +316,8 @@ static int gen6_alloc_query(struct brw_context *brw,
       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