On Thu, Aug 20, 2015 at 5:44 AM, Will Green <w...@sundivenetworks.com> wrote:
> 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 , the wiki  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.
>  https://www.freebsd.org/cgi/man.cgi?query=powerd
>  https://wiki.freebsd.org/TuningPowerConsumption
There was a working group at BSDCan this year on power management, and
what we need to / can do to bring it up to par with the modern world.
Unfortunately, I haven't had any time lately to work on it, but you
can read the notes at
In short, the goal is to add infrastructure to the kernel to support
overall power management of the system, scaling beyond cpufreq/powerd.
Looking for volunteers who could do some of this, due to my lack of
time to work on it.
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