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.
The actual implementation looks good.
So with or without the extra un-rolling the patch is:
Acked-by: Sam Ravnborg <sam@xxxxxxxxxxxx>
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@xxxxxxx>
> ---
> 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()?
>
> switch (bpp) {
> case 8:
> tab = fb_be_math(p) ? cfb_tab8_be : cfb_tab8_le;
> + tablen = 16;
> break;
> case 16:
> tab = fb_be_math(p) ? cfb_tab16_be : cfb_tab16_le;
> + tablen = 4;
> break;
> case 32:
> - 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
