Re: [PATCH 2/2] fbdev: Improve performance of sys_imageblit()

Hi

Am 17.02.22 um 12:05 schrieb Gerd Hoffmann:

...

• 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;
  }
  

How about moving the switch out of the loop, i.e.

switch (ppw) { case 4: for (j = ...) { *dst++ = colortab[(*src >> 4) & bit_mask]; *dst++ = colortab[(*src >> 0) & bit_mask]; } [ ... ] }

?

No difference. Values for the microbenchmark (rdtsc around sys_imageblit()) and the directory listing stabilize at the same numbers. I'll still go with you suggestion, because the code is more readable.

Best regards Thomas

take care, Gerd