Re: [PATCH 1/2] fbdev: Move two variable assignments in fb_alloc_cmap_gfp()

[Markus Elfring]

>> Move the assignment for the local variables “size” and “flags”
>> because the computed values were only used in a single if branch.
>
> Please do not move such variables without real need.

Is there a need to explain desirable effects better?


> It makes backporting (of this and maybe follow-up patches) much more 
> complicated

I suggest to reconsider such development concerns a bit more.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/drivers/video/fbdev/core/fbcmap.c?h=v6.4-rc3


> and the compiler will optimize it anyway.

How much do expectations fit to supported and documented software optimisations?

Regards,
Markus

Re: [PATCH 1/2] fbdev: Move two variable assignments in fb_alloc_cmap_gfp()

[Helge Deller]

On 5/23/23 22:15, Markus Elfring wrote:

From: Markus Elfring 
Date: Tue, 23 May 2023 21:30:29 +0200

Move the assignment for the local variables “size” and “flags”
because the computed values were only used in a single if branch.


Please do not move such variables without real need.
It makes backporting (of this and maybe follow-up patches) much more
complicated and the compiler will optimize it anyway.

Thanks!
Helge



Signed-off-by: Markus Elfring 
---
  drivers/video/fbdev/core/fbcmap.c | 7 ---
  1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcmap.c 
b/drivers/video/fbdev/core/fbcmap.c
index ff09e57f3c38..5c1075ed28ab 100644
--- a/drivers/video/fbdev/core/fbcmap.c
+++ b/drivers/video/fbdev/core/fbcmap.c
@@ -91,16 +91,17 @@ static const struct fb_cmap default_16_colors = {

  int fb_alloc_cmap_gfp(struct fb_cmap *cmap, int len, int transp, gfp_t flags)
  {
-   int size = len * sizeof(u16);
int ret = -ENOMEM;

-   flags |= __GFP_NOWARN;
-
if (cmap->len != len) {
+   int size;
+
fb_dealloc_cmap(cmap);
if (!len)
return 0;

+   size = len * sizeof(u16);
+   flags |= __GFP_NOWARN;
cmap->red = kzalloc(size, flags);
if (!cmap->red)
goto fail;
--
2.40.1

[PATCH 1/2] fbdev: Move two variable assignments in fb_alloc_cmap_gfp()

[Markus Elfring]

From: Markus Elfring 
Date: Tue, 23 May 2023 21:30:29 +0200

Move the assignment for the local variables “size” and “flags”
because the computed values were only used in a single if branch.

Signed-off-by: Markus Elfring 
---
 drivers/video/fbdev/core/fbcmap.c | 7 ---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcmap.c 
b/drivers/video/fbdev/core/fbcmap.c
index ff09e57f3c38..5c1075ed28ab 100644
--- a/drivers/video/fbdev/core/fbcmap.c
+++ b/drivers/video/fbdev/core/fbcmap.c
@@ -91,16 +91,17 @@ static const struct fb_cmap default_16_colors = {

 int fb_alloc_cmap_gfp(struct fb_cmap *cmap, int len, int transp, gfp_t flags)
 {
-   int size = len * sizeof(u16);
int ret = -ENOMEM;

-   flags |= __GFP_NOWARN;
-
if (cmap->len != len) {
+   int size;
+
fb_dealloc_cmap(cmap);
if (!len)
return 0;

+   size = len * sizeof(u16);
+   flags |= __GFP_NOWARN;
cmap->red = kzalloc(size, flags);
if (!cmap->red)
goto fail;
--
2.40.1