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

[Thomas Zimmermann]

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
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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