[v3,4/5] fbdev: Improve performance of cfb_imageblit()

[Thomas Zimmermann]

Hi

Am 08.03.22 um 23:52 schrieb Marek Szyprowski:
> Hi Thomas,
> 
> On 23.02.2022 20:38, Thomas Zimmermann wrote:
>> 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: Thomas Zimmermann <tzimmermann at suse.de>
>> Acked-by: Sam Ravnborg <sam at ravnborg.org>
>> Reviewed-by: Javier Martinez Canillas <javierm at redhat.com>
> This patch landed recently in linux next-20220308 as commit 0d03011894d2
> ("fbdev: Improve performance of cfb_imageblit()"). Sadly it causes a
> freeze after DRM and emulated fbdev initialization on various Samsung
> Exynos ARM 32bit based boards. This happens when kernel is compiled from
> exynos_defconfig. Surprisingly when kernel is compiled from
> multi_v7_defconfig all those boards boot fine, so this is a matter of
> one of the debugging options enabled in the exynos_defconfig. I will try
> to analyze this further and share the results. Reverting $subject on top
> of next-20220308 fixes the boot issue.

Thanks for reporting. I don't have the hardware to reproduce it and 
there's no obvious difference to the original version. It's supposed to 
be the same algorithm with a different implementation. Unless you can 
figure out the issue, we can also revert the patch easily.

Best regards
Thomas

>> ---
>>    drivers/video/fbdev/core/cfbimgblt.c | 51 +++++++++++++++++++++++-----
>>    1 file changed, 42 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/video/fbdev/core/cfbimgblt.c b/drivers/video/fbdev/core/cfbimgblt.c
>> index 01b01a279681..7361cfabdd85 100644
>> --- a/drivers/video/fbdev/core/cfbimgblt.c
>> +++ b/drivers/video/fbdev/core/cfbimgblt.c
>> @@ -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 = image->height; i--; ) {
>> -		dst = (u32 __iomem *) dst1, shift = 8; src = s;
>> +	for (i = 0; i < tablen; ++i)
>> +		colortab[i] = (tab[i] & eorx) ^ bgx;
>>    
>> -		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++; }
>> +	for (i = image->height; i--; ) {
>> +		dst = (u32 __iomem *)dst1;
>> +		src = s;
>> +
>> +		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;
>>    	}
> 
> Best regards

-- 
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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