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().
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;
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;
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++;
+ for (j = k; j; j -= jdecr, ++src) {
+ switch (ppw) {
+ case 4: /* 8 bpp */
+ *dst++ = colortab[(*src >> 4) & bit_mask];
+ *dst++ = colortab[(*src >> 0) & bit_mask];
+ break;
+ case 2: /* 16 bpp */
+ *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 */
+ *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;
--
2.34.1
