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I run an Ivy Bridge i5 3570k overclocked to 4.4 GHz. I had cpufreq set up with ondemand to perform well and scale down on low usage. In the last week or two (not sure when, really), I've noticed poor performance, particularly in games, which have become basically unplayable. I looked into it today and it seems that the CPU is running at around 2 GHz under load (running Dolphin, a Wii emulator, in this case, which now runs poorly even though it could previously sustain 60 FPS).
I then found out that cpufreq is no longer used, and pstate manages CPU power instead. I guess for some reason my system likely only started using it recently (through no action of my own other than likely a system update) even though from what I hear it should have been in the kernel about a year ago. I tried setting pstate to use the performance governor rather than powersave, which has fixed my performance issues. The cpu now ramps up to 4.4 GHz as it should, and interestingly, it does sometimes scale down to about 2.5 GHz when idle, which seems unlike what it's meant to do.
The question is, why is powersave not working as intended? To most other people, it seems like it performs basically identical to the performance governor, but I get wildly different performance from the two. It would be nice to be able to use powersave, or at least find out why it doesn't work properly (and maybe get some bugs fixed along the way) although I'm not too concerned about using the performance profile for now. Temperatures are low, as they used to be.
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The performance governor of intel pstate will scale down the frequency, I think this is working as intended. One reason is that to achieve maximum "turbo boost" on one core, the other cores must be in the C3 state or lower, so to get maximum performance out of a single thread, other unused cores actually need to slow down. The main difference between performance and powersave seems to be that performance aggressively scales up and hesitantly slows down.
But there is something fishy with intel pstate recently, especially with the powersave governor.
If a cpu intensive worker thread runs on core 0 (or core 4, which is the same physical core), everything works as intended. The core is running with max CPU clock, in my case 4.6 GHz. But iInteresting things do happen if I force the thread to another core with "taskset -p -c 3 <pid>": The frequency as shown by i7z is fluctuating wildly between 2 and 4 GHz and the worker thread performs significantly slower. Now if I run "cpupower frequency-set -g powersave" the worker thread on core 3 immediatly picks up 4.6 GHz (as it should), so powersave actually runs faster. Switching back with "cpupower frequency-set -g performance" now seems to make the performance governor work as expected. maybe a kernel bug?
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