linux-kernel - [PATCH] uvesafb,vesafb: create write-combining or write-back PAT entries

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Date:	Sat, 27 Nov 2010 14:37:37 +0100
From:	Thomas Schlichter <thomas.schlichter@....de>
To:	Michal Januszewski <spock@...too.org>
Cc:	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] uvesafb,vesafb: create write-combining or write-back PAT entries

Hi,

with an PAT-enabled kernel (tested with 2.6.35, but the problem is still 
present in current -tip), when using uvesafb or vesafb, these drivers will 
create uncached-minus PAT entries for the framebuffer memory because they use 
ioremap() (not the *_cached or *_wc variants). When the framebuffer memory 
intersects with the video RAM used by Xorg, the complete video RAM will be 
mapped uncached-minus what results in a serve performance penalty.

Here are the correct MTRR entries created by uvesafb:
schlicht@...book:~$ cat /proc/mtrr
reg00: base=0x000000000 ( 0MB), size= 2048MB, count=1: write-back
reg01: base=0x06ff00000 ( 1791MB), size= 1MB, count=1: uncachable
reg02: base=0x070000000 ( 1792MB), size= 256MB, count=1: uncachable
reg03: base=0x0d0000000 ( 3328MB), size= 16MB, count=1: write-combining

And here are the problematic PAT entries:
schlicht@...book:~$ sudo cat /sys/kernel/debug/x86/pat_memtype_list
PAT memtype list:
write-back @ 0x0-0x1000
uncached-minus @ 0x6fedd000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee3000-0x6fee4000
uncached-minus @ 0x6fee3000-0x6fee4000
uncached-minus @ 0x6fee3000-0x6fee4000
uncached-minus @ 0xd0000000-0xe0000000 <-- created by xserver-xorg
uncached-minus @ 0xd0000000-0xd1194000 <-- created by uvesafb
uncached-minus @ 0xf4000000-0xf4009000
uncached-minus @ 0xf4200000-0xf4400000
uncached-minus @ 0xf5000000-0xf5010000
uncached-minus @ 0xf5100000-0xf5104000
uncached-minus @ 0xf5400000-0xf5404000
uncached-minus @ 0xf5404000-0xf5405000
uncached-minus @ 0xf5404000-0xf5405000
uncached-minus @ 0xfed00000-0xfed01000

Therefore I created the attached patch for uvesafb which uses ioremap_wc() to 
create the correct PAT entries, as shown below:
schlicht@...book:~$ sudo cat /sys/kernel/debug/x86/pat_memtype_list
PAT memtype list:
write-back @ 0x0-0x1000
uncached-minus @ 0x6fedd000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee2000-0x6fee3000
uncached-minus @ 0x6fee3000-0x6fee4000
uncached-minus @ 0x6fee3000-0x6fee4000
uncached-minus @ 0x6fee3000-0x6fee4000
write-combining @ 0xd0000000-0xe0000000
write-combining @ 0xd0000000-0xd1194000
uncached-minus @ 0xf4000000-0xf4009000
uncached-minus @ 0xf4200000-0xf4400000
uncached-minus @ 0xf5000000-0xf5010000
uncached-minus @ 0xf5100000-0xf5104000
uncached-minus @ 0xf5400000-0xf5404000
uncached-minus @ 0xf5404000-0xf5405000
uncached-minus @ 0xf5404000-0xf5405000
uncached-minus @ 0xfed00000-0xfed01000

This results in a performance gain, objectively measurable with e.g.
x11perf -comppixwin10 -comppixwin100 -comppixwin500:
1: x11perf_xaa.log
2: x11perf_xaa_patched.log

    1 2 Operation
-------- ----------------- -----------------
124000.0 202000.0 ( 1.63) Composite 10x10 from pixmap to window
  3340.0 24400.0 ( 7.31) Composite 100x100 from pixmap to window
   131.0 1150.0 ( 8.78) Composite 500x500 from pixmap to window

You can see the serve performance gain when composing larger pixmaps to 
window.
Please consider applying the attached patches for uvesafb and vesafb.

These patches (for -tip) replace the ioremap() function with the variants 
matching the mtrr-parameter. To create "write-back" PAT entries, the 
ioremap_cache() function must be called after creating the MTRR entries, and 
the ioremap_cache() region must completely fit into the MTRR region, this is 
why the MTRR region size is now rounded up to the next power-of-two.

Signed-off-by: Thomas Schlichter <thomas.schlichter@....de>

Thank you very much!

Kind regards,
  Thomas

View attachment "vesafb.diff" of type "text/x-patch" (2418 bytes)

View attachment "uvesafb.diff" of type "text/x-patch" (2607 bytes)