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 --- drivers/video/fbdev/core/sysimgblt.c | 49 +++++++++++++++++++++------- 1 file changed, 38 insertions(+), 11 deletions(-)
diff --git a/drivers/video/fbdev/core/sysimgblt.c b/drivers/video/fbdev/core/sysimgblt.c index a4d05b1b17d7..722c327a381b 100644 --- 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;