Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 96f8e806 authored by Thomas Zimmermann's avatar Thomas Zimmermann Committed by Greg Kroah-Hartman
Browse files

fbdev: Improve performance of sys_imageblit() 



[ Upstream commit 6f29e04938bf509fccfad490a74284cf158891ce ]

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: default avatarThomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: default avatarJavier Martinez Canillas <javierm@redhat.com>
Acked-by: default avatarSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220223193804.18636-3-tzimmermann@suse.de


Stable-dep-of: c2d22806aecb ("fbdev: fix potential OOB read in fast_imageblit()")
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 7e5b7360

drivers/video/fbdev/core/sysimgblt.c

+38 −11
Original line number Diff line number Diff line
@@ -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;