Comment 26 for bug 314928

I can also confirm very choppy fullscreen flash playback and that the fix provided in the original bug report works.

Here is my /proc/mtrr before the fix:

reg00: base=0x000000000 ( 0MB), size= 1024MB, count=1: write-back
reg01: base=0x03f700000 ( 1015MB), size= 1MB, count=1: uncachable
reg02: base=0x03f800000 ( 1016MB), size= 8MB, count=1: uncachable

And my lspci -v:

00:02.0 VGA compatible controller: Intel Corporation Mobile 945GM/GMS, 943/940GML Express Integrated Graphics Controller (rev 03)
 Subsystem: Gateway 2000 Device 0205
 Flags: bus master, fast devsel, latency 0, IRQ 16
 Memory at d0300000 (32-bit, non-prefetchable) [size=512K]
 I/O ports at 1800 [size=8]
 Memory at c0000000 (32-bit, prefetchable) [size=256M]
 Memory at d0400000 (32-bit, non-prefetchable) [size=256K]
 Capabilities: <access denied>
 Kernel modules: intelfb

After doing a
sudo -s
echo "base=0xc0000000 size=0x10000000 type=write-combining" > /proc/mtrr

my /proc/mtrr now looks like this:
reg00: base=0x000000000 ( 0MB), size= 1024MB, count=1: write-back
reg01: base=0x03f700000 ( 1015MB), size= 1MB, count=1: uncachable
reg02: base=0x03f800000 ( 1016MB), size= 8MB, count=1: uncachable
reg03: base=0x0c0000000 ( 3072MB), size= 256MB, count=1: write-combining

Unfortunately the change is not preserved upon reboot, so one has to manually do this "sudo -s..." stuff with each login. (It can be automated, but still...)