Windows 7, x64, gtx 580, nvidia drivers 332.21
Short description of error
Cycles is approximately 30% slower when rendering in 2.71 compared to 2.70
I used the Mike Pan benchmark (modified, find attached the version i used), rendered via commandline with the command blender -b BMW-MikePan.blend -o C:\tmp\ -f 1
2.70a rendered in 55 seconds
2.71 rendered in 73 seconds
This is consistent with real world scenes.
I am unable to pinpoint exactly down where it happened but somewhere between revision 25ad7b4 and revision cc439f6