Comment 4 for bug 314928

I can confirm this on a DELL Inspiron 510m laptop & Jaunty, with all the latest updates. The most notable problem I experience is stuttering video through Totem (using the standard GStreamer backend, Xv output) and other media players.

Relevant lspci -vvnn output:

00:02.0 VGA compatible controller [0300]: Intel Corporation 82852/855GM Integrated Graphics Device [8086:3582] (rev 02)
 Subsystem: Dell Device [1028:0164]
 Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
 Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx+
 Latency: 0
 Interrupt: pin A routed to IRQ 11
 Region 0: Memory at f0000000 (32-bit, prefetchable) [size=128M]
 Region 1: Memory at faf80000 (32-bit, non-prefetchable) [size=512K]
 Region 2: I/O ports at c000 [size=8]
 Capabilities: <access denied>
 Kernel modules: intelfb

Current MTRR setup:

conn@inspiron:~$ cat /proc/mtrr
reg00: base=0x000000000 ( 0MB), size= 512MB, count=1: write-back
reg01: base=0x020000000 ( 512MB), size= 256MB, count=1: write-back
reg02: base=0x02ff00000 ( 767MB), size= 1MB, count=1: uncachable
reg03: base=0x0feda0000 ( 4077MB), size= 128KB, count=1: write-through

The fix:
sudo -s
echo "base=0xF0000000 size=0x08000000 type=write-combining" >| /proc/mtrr

Enabling write combining allows Totem to play 720p content with absolutely no stuttering (compared to low-resolution content stuttering without the fix). I can't say that I notice a huge increase in 3D performance, however. I won't bother to report glxgears scores, it's not an accurate tool to measure performance.