[Mesa-dev] [PATCH 12/16] i965: Use write-combine mappings where available

[Matt Turner]

Write-combine mappings give much better performance on writes than
uncached access through the GTT.
---
 src/mesa/drivers/dri/i965/brw_bufmgr.c | 69 ++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.c b/src/mesa/drivers/dri/i965/brw_bufmgr.c
index aec07e1..bbcda04 100644
--- a/src/mesa/drivers/dri/i965/brw_bufmgr.c
+++ b/src/mesa/drivers/dri/i965/brw_bufmgr.c
@@ -110,6 +110,7 @@ struct brw_bufmgr {
    struct hash_table *handle_table;
 
    bool has_llc:1;
+   bool has_mmap_wc:1;
    bool bo_reuse:1;
 };
 
@@ -701,6 +702,48 @@ brw_bo_map_cpu(struct brw_context *brw, struct brw_bo *bo, unsigned flags)
 }
 
 static void *
+brw_bo_map_wc(struct brw_context *brw, struct brw_bo *bo, unsigned flags)
+{
+   struct brw_bufmgr *bufmgr = bo->bufmgr;
+
+   pthread_mutex_lock(&bufmgr->lock);
+
+   if (!bo->map_wc) {
+      struct drm_i915_gem_mmap mmap_arg;
+
+      DBG("brw_bo_map_wc: %d (%s), map_count=%d\n",
+          bo->gem_handle, bo->name, bo->map_count);
+
+      memclear(mmap_arg);
+      mmap_arg.handle = bo->gem_handle;
+      mmap_arg.size = bo->size;
+      mmap_arg.flags = I915_MMAP_WC;
+      int ret = drmIoctl(bufmgr->fd, DRM_IOCTL_I915_GEM_MMAP, &mmap_arg);
+      if (ret != 0) {
+         ret = -errno;
+         DBG("%s:%d: Error mapping buffer %d (%s): %s .\n",
+             __FILE__, __LINE__, bo->gem_handle, bo->name, strerror(errno));
+         pthread_mutex_unlock(&bufmgr->lock);
+         return NULL;
+      }
+      bo->map_count++;
+      VG(VALGRIND_MALLOCLIKE_BLOCK(mmap_arg.addr_ptr, mmap_arg.size, 0, 1));
+      bo->map_wc = (void *) (uintptr_t) mmap_arg.addr_ptr;
+   }
+   DBG("brw_bo_map_wc: %d (%s) -> %p\n", bo->gem_handle, bo->name, bo->map_wc);
+
+   if (!(flags & MAP_ASYNC))
+      set_domain(brw, "WC mapping", bo, I915_GEM_DOMAIN_GTT,
+                 flags & MAP_WRITE ? I915_GEM_DOMAIN_GTT : 0);
+
+   bo_mark_mmaps_incoherent(bo);
+   VG(VALGRIND_MAKE_MEM_DEFINED(bo->map_wc, bo->size));
+   pthread_mutex_unlock(&bufmgr->lock);
+
+   return bo->map_wc;
+}
+
+static void *
 brw_bo_map_gtt(struct brw_context *brw, struct brw_bo *bo, unsigned flags)
 {
    struct brw_bufmgr *bufmgr = bo->bufmgr;
@@ -771,10 +814,14 @@ can_map_cpu(struct brw_bo *bo, unsigned flags)
 void *
 brw_bo_map(struct brw_context *brw, struct brw_bo *bo, unsigned flags)
 {
+   struct brw_bufmgr *bufmgr = bo->bufmgr;
+
    if (bo->tiling_mode != I915_TILING_NONE && !(flags & MAP_RAW))
       return brw_bo_map_gtt(brw, bo, flags);
    else if (can_map_cpu(bo, flags))
       return brw_bo_map_cpu(brw, bo, flags);
+   else if (bufmgr->has_mmap_wc)
+      return brw_bo_map_wc(brw, bo, flags);
    else
       return brw_bo_map_gtt(brw, bo, flags);
 }
@@ -1177,6 +1224,27 @@ brw_reg_read(struct brw_bufmgr *bufmgr, uint32_t offset, uint64_t *result)
    return ret;
 }
 
+static int
+gem_param(int fd, int name)
+{
+   drm_i915_getparam_t gp;
+   int v = -1; /* No param uses (yet) the sign bit, reserve it for errors */
+
+   memset(&gp, 0, sizeof(gp));
+   gp.param = name;
+   gp.value = &v;
+   if (drmIoctl(fd, DRM_IOCTL_I915_GETPARAM, &gp))
+      return -1;
+
+   return v;
+}
+
+static bool
+test_has_mmap_wc(int fd)
+{
+   return gem_param(fd, I915_PARAM_MMAP_VERSION) > 0;
+}
+
 /**
  * Initializes the GEM buffer manager, which uses the kernel to allocate, map,
  * and manage map buffer objections.
@@ -1209,6 +1277,7 @@ brw_bufmgr_init(struct gen_device_info *devinfo, int fd, int batch_size)
    }
 
    bufmgr->has_llc = devinfo->has_llc;
+   bufmgr->has_mmap_wc = test_has_mmap_wc(fd);
 
    init_cache_buckets(bufmgr);
 
-- 
2.10.2