Commit 0d030118 authored by Thomas Zimmermann's avatar Thomas Zimmermann
Browse files

fbdev: Improve performance of cfb_imageblit() 



Improve the performance of cfb_imageblit() by manually unrolling
the inner blitting loop and moving some invariants out. The compiler
failed to do this automatically. This change keeps cfb_imageblit()
in sync with sys_imagebit().

A microbenchmark measures the average number of CPU cycles
for cfb_imageblit() after a stabilizing period of a few minutes
(i7-4790, FullHD, simpledrm, kernel with debugging).

cfb_imageblit(), new: 15724 cycles
cfb_imageblit(): old: 30566 cycles

In the optimized case, cfb_imageblit() is now ~2x faster than before.

v3:
	* fix commit description (Pekka)

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/20220223193804.18636-5-tzimmermann@suse.de
parent 3c54c95b

drivers/video/fbdev/core/cfbimgblt.c

+42 −9
Original line number Diff line number Diff line
@@ -218,23 +218,29 @@ static inline void fast_imageblit(const struct fb_image *image, struct fb_info * 
{

	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 __iomem *dst;

	const u32 *tab = NULL;

	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--; ) {
@@ -248,15 +254,42 @@ static inline void fast_imageblit(const struct fb_image *image, struct fb_info * 
	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 = (u32 __iomem *) dst1, shift = 8; src = s;

		dst = (u32 __iomem *)dst1;

		src = s;



		for (j = k; j--; ) {

			shift -= ppw;

			end_mask = tab[(*src >> shift) & bit_mask];

			FB_WRITEL((end_mask & eorx)^bgx, dst++);

			if (!shift) { shift = 8; src++; }

		switch (ppw) {

		case 4: /* 8 bpp */

			for (j = k; j; j -= 2, ++src) {

				FB_WRITEL(colortab[(*src >> 4) & bit_mask], dst++);

				FB_WRITEL(colortab[(*src >> 0) & bit_mask], dst++);

			}

			break;

		case 2: /* 16 bpp */

			for (j = k; j; j -= 4, ++src) {

				FB_WRITEL(colortab[(*src >> 6) & bit_mask], dst++);

				FB_WRITEL(colortab[(*src >> 4) & bit_mask], dst++);

				FB_WRITEL(colortab[(*src >> 2) & bit_mask], dst++);

				FB_WRITEL(colortab[(*src >> 0) & bit_mask], dst++);

			}

			break;

		case 1: /* 32 bpp */

			for (j = k; j; j -= 8, ++src) {

				FB_WRITEL(colortab[(*src >> 7) & bit_mask], dst++);

				FB_WRITEL(colortab[(*src >> 6) & bit_mask], dst++);

				FB_WRITEL(colortab[(*src >> 5) & bit_mask], dst++);

				FB_WRITEL(colortab[(*src >> 4) & bit_mask], dst++);

				FB_WRITEL(colortab[(*src >> 3) & bit_mask], dst++);

				FB_WRITEL(colortab[(*src >> 2) & bit_mask], dst++);

				FB_WRITEL(colortab[(*src >> 1) & bit_mask], dst++);

				FB_WRITEL(colortab[(*src >> 0) & bit_mask], dst++);

			}

			break;

		}



		dst1 += p->fix.line_length;

		s += spitch;

	}