We have an R620 that showed OS-freezes, most probably due to deeper C-States allowed from the intel_idle driver from Ubuntu14.04LTS. By setting kernel boot parameter intel_idle.max_cstate=0 the lower c-states are not reached anymore, however, c0-states are not 100% (as displayed in the pcm-sensor(Intel) in ksysguard, so C1/C1E are active. I saw a power increase by 30 W (180W -> 210W) under 0 load by setting the intel_idle.max_cstate=0.
Does anybody know
1) what was the exact Errata-entry from Intel (E5-2600-v2) that caused the deeper C-state problems
2) whether the bios 2.5.2 microcode could fix something, so that I do not need the intel_idle.max_cstate=0 setting
3) what more can I do in the Bios-settings etc. to recover better performance/watt