diff mbox series

[1/2] fbdev: Improve performance of sys_fillrect()

Message ID 20220217103405.26492-2-tzimmermann@suse.de
State Superseded
Headers show
Series fbdev: Improve performance of fbdev console | expand

Commit Message

Thomas Zimmermann Feb. 17, 2022, 10:34 a.m. UTC
Improve the performance of sys_fillrect() by using word-aligned
32/64-bit mov instructions. While the code tried to implement this,
the compiler failed to create fast instructions. The resulting
binary instructions were even slower than cfb_fillrect(), which
uses the same algorithm, but operates on I/O memory.

A microbenchmark measures the average number of CPU cycles
for sys_fillrect() after a stabilizing period of a few minutes
(i7-4790, FullHD, simpledrm, kernel with debugging). The value
for CFB is given as a reference.

  sys_fillrect(), new:  26586 cycles
  sys_fillrect(), old: 166603 cycles
  cfb_fillrect():       41012 cycles

In the optimized case, sys_fillrect() is now ~6x faster than before
and ~1.5x faster than the CFB implementation.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/video/fbdev/core/sysfillrect.c | 16 +++-------------
 1 file changed, 3 insertions(+), 13 deletions(-)

Comments

Sam Ravnborg Feb. 18, 2022, 9:35 a.m. UTC | #1
Hi Thomas,

On Thu, Feb 17, 2022 at 11:34:04AM +0100, Thomas Zimmermann wrote:
> Improve the performance of sys_fillrect() by using word-aligned
> 32/64-bit mov instructions. While the code tried to implement this,
> the compiler failed to create fast instructions. The resulting
> binary instructions were even slower than cfb_fillrect(), which
> uses the same algorithm, but operates on I/O memory.
> 
> A microbenchmark measures the average number of CPU cycles
> for sys_fillrect() after a stabilizing period of a few minutes
> (i7-4790, FullHD, simpledrm, kernel with debugging). The value
> for CFB is given as a reference.
> 
>   sys_fillrect(), new:  26586 cycles
>   sys_fillrect(), old: 166603 cycles
>   cfb_fillrect():       41012 cycles
> 
> In the optimized case, sys_fillrect() is now ~6x faster than before
> and ~1.5x faster than the CFB implementation.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>

Nice optimization.
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>

> ---
>  drivers/video/fbdev/core/sysfillrect.c | 16 +++-------------
>  1 file changed, 3 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/video/fbdev/core/sysfillrect.c b/drivers/video/fbdev/core/sysfillrect.c
> index 33ee3d34f9d2..bcdcaeae6538 100644
> --- a/drivers/video/fbdev/core/sysfillrect.c
> +++ b/drivers/video/fbdev/core/sysfillrect.c
> @@ -50,19 +50,9 @@ bitfill_aligned(struct fb_info *p, unsigned long *dst, int dst_idx,
>  
>  		/* Main chunk */
>  		n /= bits;
> -		while (n >= 8) {
> -			*dst++ = pat;
> -			*dst++ = pat;
> -			*dst++ = pat;
> -			*dst++ = pat;
> -			*dst++ = pat;
> -			*dst++ = pat;
> -			*dst++ = pat;
> -			*dst++ = pat;
> -			n -= 8;
> -		}
> -		while (n--)
> -			*dst++ = pat;
> +		memset_l(dst, pat, n);
> +		dst += n;
> +
>  		/* Trailing bits */
>  		if (last)
>  			*dst = comp(pat, *dst, last);
> -- 
> 2.34.1
diff mbox series

Patch

diff --git a/drivers/video/fbdev/core/sysfillrect.c b/drivers/video/fbdev/core/sysfillrect.c
index 33ee3d34f9d2..bcdcaeae6538 100644
--- a/drivers/video/fbdev/core/sysfillrect.c
+++ b/drivers/video/fbdev/core/sysfillrect.c
@@ -50,19 +50,9 @@  bitfill_aligned(struct fb_info *p, unsigned long *dst, int dst_idx,
 
 		/* Main chunk */
 		n /= bits;
-		while (n >= 8) {
-			*dst++ = pat;
-			*dst++ = pat;
-			*dst++ = pat;
-			*dst++ = pat;
-			*dst++ = pat;
-			*dst++ = pat;
-			*dst++ = pat;
-			*dst++ = pat;
-			n -= 8;
-		}
-		while (n--)
-			*dst++ = pat;
+		memset_l(dst, pat, n);
+		dst += n;
+
 		/* Trailing bits */
 		if (last)
 			*dst = comp(pat, *dst, last);