Could you please include your system information as requested at https://github.com/ValveSoftware/steam-for-linux#reporting-issues

One of the more common issues with the in-game performance has been with multi-core rendering. Have you tried disabling that and seeing how things perform?

Processor Information:
Vendor: AuthenticAMD
Speed: 4000 Mhz
8 logical processors
8 physical processors
HyperThreading: Unsupported
FCMOV: Supported
SSE2: Supported
SSE3: Supported
SSSE3: Supported
SSE4a: Supported
SSE41: Supported
SSE42: Supported

Network Information:
Network Speed:

Operating System Version:
Ubuntu 13.04 (64 bit)
Kernel Name: Linux
Kernel Version: 3.8.0-19-generic
X Server Vendor: The X.Org Foundation
X Server Release: 11303000
X Window Manager: Compiz
Steam Runtime Version: steam-runtime-release-i386_2013-04-16

Video Card:
Driver: ATI Technologies Inc. AMD Radeon HD 7900 Series

Driver Version:  4.2.12217 Compatibility Profile Context 12.10.17
Desktop Color Depth: 24 bits per pixel
Monitor Refresh Rate: 59 Hz
VendorID:  0x1002
DeviceID:  0x679a
Number of Monitors:  1
Number of Logical Video Cards:  1
Primary Display Resolution:  1920 x 1200
Desktop Resolution: 1920 x 1200
Primary Display Size: 23.35" x 14.61"  (27.52" diag)
                                        59.3cm x 37.1cm  (69.9cm diag)
Primary VRAM Not Detected

Sound card:
Audio device: Realtek ALC892

Memory:
RAM: 15996 Mb

I will try disabling multicore rendering.

Disabling multicore rendering has no effect. TF2's main menu is extremely laggy, and in the game it's even worse. Steam overlay is, of course, as laggy as ever. Texture corruption galore in Source games. It's that texture glitch where textures flicker between being really dark and really bright while you are moving about the map.

Same crappy glitches and lag using Xfce instead of Unity. TF2 has it the worst. It's to the point where the main menu is laggy, once you are in-game the mouse moves in slow motion and framerate is about 1-2 FPS.

Same here, TF2 is unplayable with Linux. Maybe I should go back to using Wine :P

I have exactly the same problem with my Phenom II 965 and my Radeon HD 5870. Steam overlay cause a huge game lag (10fps ...) even if i get a single notification when i play! And most of the games are absolutely not playable. Especially Serious Sam 3 , Killing Floor, TF2, Costume Quest and LFD2. CS:S and older Games like HL, HL2 do work but also stutter on some maps / areas...

Sorry for my English! I use the latest Catalyst 13.4 drivers ....

Processor Information:
Vendor: AuthenticAMD
Speed: 3400 Mhz
4 logical processors
4 physical processors
HyperThreading: Unsupported
FCMOV: Supported
SSE2: Supported
SSE3: Supported
SSSE3: Unsupported
SSE4a: Supported
SSE41: Unsupported
SSE42: Unsupported

Network Information:
Network Speed:

Operating System Version:
Ubuntu 13.04 (64 bit)
Kernel Name: Linux
Kernel Version: 3.9.0-030900-generic
X Server Vendor: The X.Org Foundation
X Server Release: 11303000
X Window Manager: Compiz
Steam Runtime Version: steam-runtime-release-i386_2013-04-16

Video Card:
Driver: ATI Technologies Inc. ATI Radeon HD 5800 Series

Driver Version:  4.2.12217 Compatibility Profile Context 12.104
Desktop Color Depth: 24 bits per pixel
Monitor Refresh Rate: 59 Hz
VendorID:  0x1002
DeviceID:  0x6898
Number of Monitors:  1
Number of Logical Video Cards:  1
Primary Display Resolution:  1920 x 1080
Desktop Resolution: 1920 x 1080
Primary Display Size: 20,91" x 11,77"  (23,98" diag)
                                        53,1cm x 29,9cm  (60,9cm diag)
Primary VRAM Not Detected

Sound card:
Audio device: VIA VT1708S

Memory:
RAM: 7985 Mb

Miscellaneous:
UI Language: English
LANG: de_AT.UTF-8
Microphone: Not set
Total Hard Disk Space Available: 1328082 Mb
Largest Free Hard Disk Block: 903795 Mb

Installed software:

Recent Failure Reports:
Wed May 15 06:41:59 2013 GMT: file ''/tmp/dumps/assert_20130515084159_1.dmp'', upload no: ''HTTP response code said error''
Wed May 15 10:24:21 2013 GMT: file ''/tmp/dumps/assert_20130515122417_1.dmp'', upload yes: ''CrashID=bp-e9e6792c-824f-4663-bd18-269a02130515''
Wed May 15 10:25:03 2013 GMT: file ''/tmp/dumps/assert_20130515122456_1.dmp'', upload yes: ''CrashID=bp-fce95487-7eba-45c5-bf53-76bf72130515''
Wed May 15 12:55:31 2013 GMT: file ''/tmp/dumps/assert_20130515145525_1.dmp'', upload yes: ''CrashID=bp-a1b1c955-9bd9-4aeb-b510-b4b182130515''
Wed May 15 13:40:26 2013 GMT: file ''/tmp/dumps/assert_20130515154018_1.dmp'', upload yes: ''CrashID=bp-922dc220-2ff3-4086-8663-e2b9e2130515''

Meanwhile I see Catalyst 13.6 Beta is about to get uploaded publicly. However, for an entire month in absence from the last driver release for Linux, the changelog is embarrassingly small and it really doesn't fix much.

Released: http://www2.ati.com/drivers/beta/amd-driver-installer-catalyst-13-6-beta-x86.x86_64.zip

Highlights of the AMD Catalyst™ 13.6 Beta Driver for Linux:
This release of AMD Catalyst™ Linux introduces support for the following new features:

Ubuntu 13.04 Production Support
Xserver 1.14 Support
GLX_EXT_buffer_age extension support
Resolved Issues:

[371937] Fix black screen while entering Team Fortress 2 under cinnamon desktop environment
[366812] Fix tearing for some OpenGL applications with VSYNC on or off
[373575] Fix taskbar missing after UVD playback on Ubuntu 12.04
[370955] Fix corruption in Team Fortress 2 when running Dustbowl map
[377199] Fix the error for APL initialization failure
[378086] Fix screen corruption when kill X on Ubuntu 13.04
[374657] Fix some WebGL conformance test failures
[377379] Fix the regression of performance drop with XBMC for UVD playback

I'm reporting that I have a solution for many issues now.

• I am currently running Ubuntu 13.10 development branch with Unity as my DE.
• I have installed a lowlatency linux kernel, this solved all my audio latency and input lag (except TF2 in online servers).
• Currently using fglrx-13 from xorg edgers, and source games now run better.

What's not fixed:

• Graphics performance is still greatly lacking in comparison to Windows
• Don't use AA unless you want to kill your framerates
• TF2 is only playable offline with bots. In live servers with real players, there is EXTREME input lag and EXTREMELY bad framerates. Enabling host_thread_mode 1; r_threaded* 1 improves input lag drastically, but does not fix it.

I want to report that I too am having exactly the same problems. L4D2 is not playable. I get input lag and framerate drops. Sometimes my controls will actually become "stuck" auto running in the last direction that I pressed. I can also confirm that playing online is much worse than playing single-player locally with bots. I can run at 2560x1440 with everything jacked up to the max and stay at 60hz (vertical sync) without any drops whatsoever in windows 8, (I really don't like having to boot down into windows). I suspect that the catalyst drivers are to blame, but help from any angle would be appreciated.

Linux Mint 15 (Based on Ubuntu 13.04 "Raring")
Intel Core i5-4670K Haswell CPU @ 3.40GH
Radeon 7850 (AMD Catalyst Drivers 13.4 amd64 version)
16GB Ram

It might also be worth mentioning that I run dual 2560x1440 Dell UltraSharp Monitors

Yeah I can't even get 10FPS in TF2 with a 7950 at 1920x1200 with one monitor, I really doubt you'll get anywhere with that 7850 anytime soon. There is hope, however. July 31st is when Catalyst 13.7 releases which 'might' finally give us good drivers. If you are religious you might want to pray day and night that their programmers will surprise us loll. Linux kernel 3.11 might also have good radeonsi open source drivers. Right now the only way to get open source drivers to work with HD 7xxx in Ubuntu is to install a special ppa and make sure you don't have anything from xorg-edgers installed. I'll also add that open source radeonsi installed this way does not support s3tc textures.

I'm reporting that with Catalyst 13.8 Beta installed, TF2 and all other Source games are finally playable. I just tried out TF2 in two games on a full 24 player stock server (real people, not bots), and I had on average ~100FPS. There were some times in crowded areas that it dropped to ~60FPS and in close spaces with few players around it was 200+ FPS.

There wasn't any lag, although the audio is out of sync (assuming pulseaudio issue) and oddly very bass-heavy for some reason, which may not be related at all. There is a bit of framerate stutter here and there, and steam overlay still causes a massive FPS hit to the teens. It is at least playable.

As for corruption, I have not seen any yet. DODS plays fine, besides the audio lag by pulseaudio.

Left 4 Dead 2 still unplayable for me (unfortunately). It is an improvement, but I still have to boot into windows to play (where I get an unwavering 60fps with vertical refresh rate on, Radeon 7850 - 2560x1440 with all settings maxed). Before, there were all manner of problems with the linux drivers. Now, the only issue appears to be a slow, laggy framerate (~17fps). Changing the resolution and quality settings really doesn't seem to change the FPS or playability by very much, so I assume that the issue lies in other details. Anyone else still unable to play L4D2 with the new 3.8 beta drivers?

Nothing really changed for me with TF2 on HD5670. Maybe a few more fps in areas simple to render.
A good example are minecraft maps.
But sweeping the view past a 'complex' texture area will cause the rendering lagging utterly bad delayed.
It feelds like dragging the mouse through a barrel of tar.

Also, Antialiasing still doesn't seem to work at all in 3D mode in-game, nor does the key assignment for

KP_ENTER (known issue for about a year now - but that's a different story).
As of late, some update seems to have introduced a nasty bug, that causes random TF2 crashes and item server inaccessibility.

Steam's support suxx bigtimes, that's for sure.
Getting serious answers, yet solutions seems next to impossible - if any at all.
Plus, they seem to be officially refusing to accept support tickets for Linux in the support area as a rule.

If not for HL3, I wouldn't be very interested to buy any more Valve games at this point.
And if not for potential upcoming Linux support, I wouldn't care much about Steam at all.
Let's see, if it doesn't turn out to be a marketing gag in the end.

So far, I fail to see a significant increase of AAA titles to be released for Steam on Linux, as I fail to see a flawlessly working system for established titles - still. Honestly, I've expected more.

I'm using Catalyst 13.11 with kernel 3.12-rc6 right now on Ubuntu 13.04 and performance is largely solved. I'm able to play games very smoothy with 120-300 FPS at all times, without AA of course. This is a first with my HD 7950.

ATI Pitcairn PRO [Radeon HD 7850]
Ubuntu Raring
Catalyst Drivers 13.11-beta
Linux version 3.8.0-31-generic

My overall performance and experience is still the same as 13.4. LFD2 is still completely unplayable. I cannot log into an XServer multiple times under different accounts (lock screen and sign in as different user). Sometimes, I have to reboot the machine when logging off and signing in as a new user because the XServer will not restart. 13.7 beta drivers were too unstable and often crashed the XServer outright in the middle of a session.

I am still very unsatisfied. I would purchase an Nvidia card if I had to do it over again.

Upgrade from kernel 3.8 to kernel 3.12 and a lot of your problems will be solved.

cd /tmp
wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.12-rc6-saucy/linux-headers-3.12.0-031200rc6-generic_3.12.0-031200rc6.201310191635_amd64.deb
wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.12-rc6-saucy/linux-headers-3.12.0-031200rc6_3.12.0-031200rc6.201310191635_all.deb
wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.12-rc6-saucy/linux-image-3.12.0-031200rc6-generic_3.12.0-031200rc6.201310191635_amd64.deb
sudo dpkg -i linux*.deb

If you're using Ubuntu you should be install fglrx via deb.

https://www.copy.com/s/DctT73MTnQM2/Catalyst 13.11

+1 Same bug.
Ubuntu 12.04.3 Linux 3.8

With the new Catalyst 13.11 Beta 6, gl_finish 1 is no longer required.

Testing with kernel 3.13 and the latest open source drivers from Oibaf in Ubuntu 14.04, TF2 and other games run really well.

• FPS is around 100-300 but there are frame latency issues causing stuttering at times.
• Reducing texture quality reduces the amount of stuttering.

I guess all the open source drivers need now is VRAM optimizations, GLAMOR optimizations, and more OpenGL features (currently only supports OpenGL 3.0), with other general bug fixes.