Hi Sam
Am 18.02.22 um 11:14 schrieb Sam Ravnborg:
Hi Thomas,
On Thu, Feb 17, 2022 at 11:34:05AM +0100, Thomas Zimmermann wrote:
Improve the performance of sys_imageblit() by manually unrolling the inner blitting loop and moving some invariants out. The compiler failed to do this automatically. The resulting binary code was even slower than the cfb_imageblit() helper, which uses the same algorithm, but operates on I/O memory.
It would be super to have the same optimization done to cfb_imageblit(), to prevent that the two codebases diverge more than necessary. Also I think cfb_ version would also see a performance gain from this.
Yes, I can do that.
The actual implementation looks good. So with or without the extra un-rolling the patch is: Acked-by: Sam Ravnborg sam@ravnborg.org
One small nit belwo.
Sam
A microbenchmark measures the average number of CPU cycles for sys_imageblit() 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_imageblit(), new: 25934 cycles sys_imageblit(), old: 35944 cycles cfb_imageblit(): 30566 cycles
In the optimized case, sys_imageblit() is now ~30% faster than before and ~20% faster than cfb_imageblit().
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de
drivers/video/fbdev/core/sysimgblt.c | 51 +++++++++++++++++++++------- 1 file changed, 39 insertions(+), 12 deletions(-)
diff --git a/drivers/video/fbdev/core/sysimgblt.c b/drivers/video/fbdev/core/sysimgblt.c index a4d05b1b17d7..d70d65af6fcb 100644 --- a/drivers/video/fbdev/core/sysimgblt.c +++ b/drivers/video/fbdev/core/sysimgblt.c @@ -188,23 +188,32 @@ static void fast_imageblit(const struct fb_image *image, struct fb_info *p, { u32 fgx = fgcolor, bgx = bgcolor, bpp = p->var.bits_per_pixel; u32 ppw = 32/bpp, spitch = (image->width + 7)/8;
- u32 bit_mask, end_mask, eorx, shift;
- u32 bit_mask, eorx; const char *s = image->data, *src; u32 *dst;
- const u32 *tab = NULL;
- int i, j, k;
- const u32 *tab;
- size_t tablen;
- u32 colortab[16];
- int i, j, k, jdecr;
- if ((uintptr_t)dst1 % 8)
return;This check is new - and should not trigger ever. Maybe add an unlikely and a WARN_ON_ONCE()?
I think I can remove this test. It was supposed to tell the compiler that dst1 is 8-aligned, but I don't think it worked.
Best regards Thomas
switch (bpp) { case 8: tab = fb_be_math(p) ? cfb_tab8_be : cfb_tab8_le;
tablen = 16;tablen = 4;
- default: tab = cfb_tab32;
tablen = 2;break;
default:
return;}
for (i = ppw-1; i--; ) {
@@ -217,19 +226,37 @@ static void fast_imageblit(const struct fb_image *image, struct fb_info *p, bit_mask = (1 << ppw) - 1; eorx = fgx ^ bgx; k = image->width/ppw;
- jdecr = 8 / ppw;
- for (i = 0; i < tablen; ++i)
colortab[i] = (tab[i] & eorx) ^ bgx;This code could have been embedded with the switch (bpp) { That would have made some sense I think. But both ways works, so this was just a small observation.
Sam