[PATCH 1/1 2.6.13] framebuffer: bit_putcs() optimization for 8x* fonts

[Knut Petersen <Knut_Petersen@t-online.de>]

This trivial patch gives a performance boost to the framebuffer console

Constructing the bitmaps that are given to the bitblit functions of the 
framebuffer
drivers is time consuming. Here we avoide a call to the slow 
fb_pad_aligned_buffer().
The patch replaces that call with a simple but much more efficient 
bytewise copy.

The kernel spends a significant time at this place if you use 8x* fonts. 
Every
pixel displayed on your screen is prepared here.

Some benchmark results:

Displaying a file of 2000 lines with 160 characters each takes 889 ms 
system
time using  cyblafb on my system  (I´m using a 1280x1024 video mode,
resulting in a 160x64 character console)

Displaying the same file with the enclosed patch applied to 2.6.13 only 
takes
760 ms system time, saving 129 ms or 14.5%.

Font widths other than 8 are not affected.

The advantage and correctness of this patch should be obvious.

Signed-off-by: Knut Petersen <Knut_Petersen@t-online.de>

diff -uprN -X linux/Documentation/dontdiff -x '*.bak' -x '*.ctx' linuxorig/drivers/video/console/bitblit.c linux/drivers/video/console/bitblit.c
--- linuxorig/drivers/video/console/bitblit.c	2005-08-29 01:41:01.000000000 +0200
+++ linux/drivers/video/console/bitblit.c	2005-08-30 17:19:57.000000000 +0200
@@ -114,7 +114,7 @@ static void bit_putcs(struct vc_data *vc
	unsigned int scan_align = info->pixmap.scan_align - 1;
	unsigned int buf_align = info->pixmap.buf_align - 1;
	unsigned int shift_low = 0, mod = vc->vc_font.width % 8;
-	unsigned int shift_high = 8, pitch, cnt, size, k;
+	unsigned int shift_high = 8, pitch, cnt, size, i, k;
	unsigned int idx = vc->vc_font.width >> 3;
	unsigned int attribute = get_attribute(info, scr_readw(s));
	struct fb_image image;
@@ -175,7 +175,11 @@ static void bit_putcs(struct vc_data *vc
					src = buf;
				}

-				fb_pad_aligned_buffer(dst, pitch, src, idx, image.height);
+				if (idx == 1)
+					for(i=0; i < image.height; i++)
+						dst[pitch*i] = src[i];
+				else
+					fb_pad_aligned_buffer(dst, pitch, src, idx, image.height);
				dst += width;
			}
		}


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