I’ve been thinking about CPU performance and power management on FreeBSD 
recently. As a user it seems like there has been little activity in this area 
and I wanted to try and understand what the situation was.

From the publicly available information on powerd [1], the wiki [2] and my 
attempts to optimize hardware power/performance; it seems the current approach 
is quite old and laptop-focused. Recent CPU designs can control the state and 
frequency of individual cores very quickly. In the case of a single heavy 
thread, a multicore CPU might power-gate all but one core so the active core 
can be pushed to a higher frequency. This doesn’t seem to be possible on 
FreeBSD at the moment: powerd is userland (~250 ms poll) and can only control 
the frequency of all cores together.

I understand this opens a can of worms as the CPU core states, frequency and 
scheduler would all need to co-operate. However, I think it’s important that 
this does happen. Without this functionality FreeBSD is leaving performance on 
the table and consuming more power than other operating systems. At BSDCan I 
heard that there was work going on for arm systems, but didn’t manage to get 
any details and whether it was relevant to amd64 too. 


PS. I was interested to see Intel announce at IDF that they'll be working with 
open source projects to implement "Speed Shift Technology”, which leaves 
responsibility for p-state management on the CPU.

[1] https://www.freebsd.org/cgi/man.cgi?query=powerd
[2] https://wiki.freebsd.org/TuningPowerConsumption

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