Gnome Shell performance degrades over time

[Alessandro Crismani <alessandro crismani gmail com>]

Hi everybody,

I've been using Gnome Shell for a long time know. My Laptop is a Lenovo T420s, 
which comes with an integrated HD3000 Sandy Bridge (SNB) graphic adapter and a 
i5 2520 CPU.

Lately, the performance of the Shell has increased and going to activities is 
smooth, compared to old times where SNB was performing awful. However, after 
some time the scaling effect "gets corrupted" and slows down. It seems like 
less frames are shown and going to the activity view becomes a frustrating 
experience, hurting my concentration. This happens even if I don't use the 
laptop and leave it idle.

I've tried many combinations of software to see if something solved it. More 
particularly, I've tried all the possible combinations between (running Arch 
Linux, if that matetrs):

Kernel 3.0.x (where x was the stable minor version at different points in 
time)
Kernel 3.1.rcx
Kernel 3.1.0

Mesa 7.10.4
Mesa 7.11.0
Mesa from the master tree as of last week (and some other older snapshots)

xf86-video-intel 2.15
xf86-video-intel 2.16
xf86-video-intel from the master tree as of last week

No combinations were found to work reliably after some time. In particular, if 
I leave the laptop idle without screen-lock or suspend enabled, when I come 
back the shell is slower than when I left.

Is this a known behaviour. Does anyone else see this on Sandy Bridge equipped 
laptops or is it only me?

Last, but more important, how can I help debugging this? I've got no idea 
about which logs might be useful: memory and CPU are under control both when 
animations are fluid and when they are "corrupted". I am enclosing my lspci as 
a starting point:

alessandro at alessandro-thinky in ~ 
$ lspci
00:00.0 Host bridge: Intel Corporation 2nd Generation Core Processor Family 
DRAM Controller (rev 09)
00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core 
Processor Family Integrated Graphics Controller (rev 09)
00:16.0 Communication controller: Intel Corporation 6 Series Chipset Family 
MEI Controller #1 (rev 04)
00:19.0 Ethernet controller: Intel Corporation 82579LM Gigabit Network 
Connection (rev 04)
00:1a.0 USB Controller: Intel Corporation 6 Series Chipset Family USB Enhanced 
Host Controller #2 (rev 04)
00:1b.0 Audio device: Intel Corporation 6 Series Chipset Family High 
Definition Audio Controller (rev 04)
00:1c.0 PCI bridge: Intel Corporation 6 Series Chipset Family PCI Express Root 
Port 1 (rev b4)
00:1c.1 PCI bridge: Intel Corporation 6 Series Chipset Family PCI Express Root 
Port 2 (rev b4)
00:1c.3 PCI bridge: Intel Corporation 6 Series Chipset Family PCI Express Root 
Port 4 (rev b4)
00:1c.4 PCI bridge: Intel Corporation 6 Series Chipset Family PCI Express Root 
Port 5 (rev b4)
00:1d.0 USB Controller: Intel Corporation 6 Series Chipset Family USB Enhanced 
Host Controller #1 (rev 04)
00:1f.0 ISA bridge: Intel Corporation 6 Series Chipset Family LPC Controller 
(rev 04)
00:1f.2 SATA controller: Intel Corporation 6 Series Chipset Family 6 port SATA 
AHCI Controller (rev 04)
00:1f.3 SMBus: Intel Corporation 6 Series Chipset Family SMBus Controller (rev 
04)
03:00.0 Network controller: Intel Corporation Centrino Ultimate-N 6300 (rev 
2c)
05:00.0 System peripheral: Ricoh Co Ltd Device e823 (rev 04)
0d:00.0 USB Controller: NEC Corporation uPD720200 USB 3.0 Host Controller (rev 
04)


Thanks to anybody who has even the slightest idea on what is going on.
Cheers,
Alessandro