[v6,07/11] drm/v3d: Reduce the alignment of the node allocation

Commit Message

Maíra Canal Sept. 23, 2024, 1:55 p.m. UTC

Currently, we are using an alignment of 128 kB to insert a node, which
ends up wasting memory as we perform plenty of small BOs allocations
(<= 4 kB). We require that allocations are aligned to 128Kb so for any
allocation smaller than that, we are wasting the difference.

This implies that we cannot effectively use the whole 4 GB address space
available for the GPU in the RPi 4. Currently, we can allocate up to
32000 BOs of 4 kB (~140 MB) and 3000 BOs of 400 kB (~1,3 GB). This can be
quite limiting for applications that have a high memory requirement, such
as vkoverhead [1].

By reducing the page alignment to 4 kB, we can allocate up to 1000000 BOs
of 4 kB (~4 GB) and 10000 BOs of 400 kB (~4 GB). Moreover, by performing
benchmarks, we were able to attest that reducing the page alignment to
4 kB can provide a general performance improvement in OpenGL
applications (e.g. glmark2).

Therefore, this patch reduces the alignment of the node allocation to 4
kB, which will allow RPi users to explore the whole 4GB virtual
address space provided by the hardware. Also, this patch allow users to
fully run vkoverhead in the RPi 4/5, solving the issue reported in [1].

[1] https://github.com/zmike/vkoverhead/issues/14

Signed-off-by: Maíra Canal <[e-mail]>
Reviewed-by: Iago Toral Quiroga <[e-mail]>
---
 drivers/gpu/drm/v3d/v3d_bo.c  | 2 +-
 drivers/gpu/drm/v3d/v3d_drv.h | 2 --
 2 files changed, 1 insertion(+), 3 deletions(-)

Patch

diff --git a/drivers/gpu/drm/v3d/v3d_bo.c b/drivers/gpu/drm/v3d/v3d_bo.c
index ecb80fd75b1a..427a1c405b19 100644
--- a/drivers/gpu/drm/v3d/v3d_bo.c
+++ b/drivers/gpu/drm/v3d/v3d_bo.c
@@ -123,7 +123,7 @@  v3d_bo_create_finish(struct drm_gem_object *obj)
 	 */
 	ret = drm_mm_insert_node_generic(&v3d->mm, &bo->node,
 					 obj->size >> V3D_MMU_PAGE_SHIFT,
-					 GMP_GRANULARITY >> V3D_MMU_PAGE_SHIFT, 0, 0);
+					 SZ_4K >> V3D_MMU_PAGE_SHIFT, 0, 0);
 	spin_unlock(&v3d->mm_lock);
 	if (ret)
 		return ret;
diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/v3d_drv.h
index 41b09c828848..82d6e869dd41 100644
--- a/drivers/gpu/drm/v3d/v3d_drv.h
+++ b/drivers/gpu/drm/v3d/v3d_drv.h
@@ -19,8 +19,6 @@  struct clk;
 struct platform_device;
 struct reset_control;
 
-#define GMP_GRANULARITY (128 * 1024)
-
 #define V3D_MMU_PAGE_SHIFT 12
 
 #define V3D_MAX_QUEUES (V3D_CPU + 1)