[PATCH] drm/vmwgfx: Don't memcmp equivalent pointers

[PATCH] drm/vmwgfx: Don't memcmp equivalent pointers

[Ian Forbes]

These pointers are frequently the same and memcmp does not compare the pointers
before comparing their contents so this was wasting cycles comparing 16 KiB of
memory which will always be equal.

Fixes: bb6780aa5a1d9 ("drm/vmwgfx: Diff cursors when using cmds")
Signed-off-by: Ian Forbes <ian.forbes@broadcom.com>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
index cd4925346ed4..fbcce84e2f4c 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
@@ -216,7 +216,7 @@ static bool vmw_du_cursor_plane_has_changed(struct vmw_plane_state *old_vps,
 	new_image = vmw_du_cursor_plane_acquire_image(new_vps);
 
 	changed = false;
-	if (old_image && new_image)
+	if (old_image && new_image && (old_image != new_image))
 		changed = memcmp(old_image, new_image, size) != 0;
 
 	return changed;
-- 
2.34.1

Re: [PATCH] drm/vmwgfx: Don't memcmp equivalent pointers

[Zack Rusin]

On Thu, Mar 28, 2024 at 3:31 PM Ian Forbes <ian.forbes@broadcom.com> wrote:
>
> These pointers are frequently the same and memcmp does not compare the pointers
> before comparing their contents so this was wasting cycles comparing 16 KiB of
> memory which will always be equal.
>
> Fixes: bb6780aa5a1d9 ("drm/vmwgfx: Diff cursors when using cmds")
> Signed-off-by: Ian Forbes <ian.forbes@broadcom.com>
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_kms.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> index cd4925346ed4..fbcce84e2f4c 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> @@ -216,7 +216,7 @@ static bool vmw_du_cursor_plane_has_changed(struct vmw_plane_state *old_vps,
>         new_image = vmw_du_cursor_plane_acquire_image(new_vps);
>
>         changed = false;
> -       if (old_image && new_image)
> +       if (old_image && new_image && (old_image != new_image))
>                 changed = memcmp(old_image, new_image, size) != 0;
>
>         return changed;
> --
> 2.34.1
>

The patch looks good but please use "dim checkpatch" and fix the
issues it found. For the "Fixes:" line you also want to use "dim
fixes".

z

[PATCH v2] drm/vmwgfx: Don't memcmp equivalent pointers

[Ian Forbes]

These pointers are frequently the same and memcmp does not compare the
pointers before comparing their contents so this was wasting cycles
comparing 16 KiB of memory which will always be equal.

Fixes: bb6780aa5a1d ("drm/vmwgfx: Diff cursors when using cmds")
Signed-off-by: Ian Forbes <ian.forbes@broadcom.com>
Cc: <stable@vger.kernel.org> # v6.2+
---
v2: Fix code and commit message formatting.
--
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
index cd4925346ed4..ef0af10c4968 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
@@ -216,7 +216,7 @@ static bool vmw_du_cursor_plane_has_changed(struct vmw_plane_state *old_vps,
 	new_image = vmw_du_cursor_plane_acquire_image(new_vps);
 
 	changed = false;
-	if (old_image && new_image)
+	if (old_image && new_image && old_image != new_image)
 		changed = memcmp(old_image, new_image, size) != 0;
 
 	return changed;
-- 
2.34.1