My issue with Left 4 Dead 2 on Steam has been ongoing for more than a year already. When I submitted a bug report to GitHub due to suspicion that Multicore Rendering (MR) might be the case one support guy replied and re-directed me to a MESA tracker of some kind which I wasn't able to find.
I don't even bother reporting the issue to VALVe anymore as they seem to care less and less with their automated responses, completely ignoring my need for a fix while building their Linux OS.
To sum this up: I have an issue with Multicore Rendering due to which I am unable to play Left 4 Dead 2 on Linux (Ubuntu 14.04 x64) with my Intel Ironlake Mobile graphics chipset, while the same game on the same laptop running Windows 7 Ultimate x64 runs totally fine.
I would need guidance on how to report this to that particular MESA tracker from where a fix could be pushed.
Read more here:
The original report
My report based on suggestion