fbdev: Improve performance of sys_imageblit()

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.

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().

v2:
	* move switch out of inner loop (Gerd)
	* remove test for alignment of dst1 (Sam)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220223193804.18636-3-tzimmermann@suse.de

diff --git a/drivers/video/fbdev/core/sysimgblt.c b/drivers/video/fbdev/core/sysimgblt.c
index a4d05b1b17d7da6dfdebcf6c7df3f538cbb982e6..722c327a381bd49af5d8c41171c67888485fbbed 100644 (file)
--- a/drivers/video/fbdev/core/sysimgblt.c
+++ b/drivers/video/fbdev/core/sysimgblt.c
@@ -188,23 +188,29 @@ 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;
+       const u32 *tab;
+       size_t tablen;
+       u32 colortab[16];
        int i, j, k;
 
        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--; ) {
@@ -218,19 +224,40 @@ static void fast_imageblit(const struct fb_image *image, struct fb_info *p,
        eorx = fgx ^ bgx;
        k = image->width/ppw;
 
+       for (i = 0; i < tablen; ++i)
+               colortab[i] = (tab[i] & eorx) ^ bgx;
+
        for (i = image->height; i--; ) {
                dst = dst1;
-               shift = 8;
                src = s;
 
-               for (j = k; j--; ) {
-                       shift -= ppw;
-                       end_mask = tab[(*src >> shift) & bit_mask];
-                       *dst++ = (end_mask & eorx) ^ bgx;
-                       if (!shift) {
-                               shift = 8;
-                               src++;
+               switch (ppw) {
+               case 4: /* 8 bpp */
+                       for (j = k; j; j -= 2, ++src) {
+                               *dst++ = colortab[(*src >> 4) & bit_mask];
+                               *dst++ = colortab[(*src >> 0) & bit_mask];
+                       }
+                       break;
+               case 2: /* 16 bpp */
+                       for (j = k; j; j -= 4, ++src) {
+                               *dst++ = colortab[(*src >> 6) & bit_mask];
+                               *dst++ = colortab[(*src >> 4) & bit_mask];
+                               *dst++ = colortab[(*src >> 2) & bit_mask];
+                               *dst++ = colortab[(*src >> 0) & bit_mask];
+                       }
+                       break;
+               case 1: /* 32 bpp */
+                       for (j = k; j; j -= 8, ++src) {
+                               *dst++ = colortab[(*src >> 7) & bit_mask];
+                               *dst++ = colortab[(*src >> 6) & bit_mask];
+                               *dst++ = colortab[(*src >> 5) & bit_mask];
+                               *dst++ = colortab[(*src >> 4) & bit_mask];
+                               *dst++ = colortab[(*src >> 3) & bit_mask];
+                               *dst++ = colortab[(*src >> 2) & bit_mask];
+                               *dst++ = colortab[(*src >> 1) & bit_mask];
+                               *dst++ = colortab[(*src >> 0) & bit_mask];
                        }
+                       break;
                }
                dst1 += p->fix.line_length;
                s += spitch;