DragonFly and Hardware P states in Skylake

Sepherosa Ziehau sepherosa at gmail.com
Tue Jul 4 18:41:38 PDT 2017


We by default turn on the HW coordination.  For most of the modern
Intel CPUs, the P-state setting, hw.acpi.cpu.px_domX, only puts the
upper limit of the CPUs frequency; e.g. CPU may run @1000Mhz even if
the P-state is set to 2000Mhz, when the system is idle.  As far as I
tested, most of the power saving of the Intel CPUs are from deep
C-state instead of P-state (see powerd man page, -c option).  And I
normally disable CPU frequency adjustment by passing -f to powerd.

You can check your CPU running frequency w/ 'systat -sens 1'; I think
aperf is in GENERIC kernel.


On Wed, Jul 5, 2017 at 1:33 AM, Brandon Werner <am_dxer at fastmail.fm> wrote:
> Hello,
> I recently got  a new machine with Skylake and one of the technologies advertised is hardware Pstates. From what I could tell Linux and Windows support this technology but I couldn't find anything about the BSD's. I must admit I don't clearly understand the technology but I guess my questions are basically whether DragomFly supports these and if not will battery life be worse. Also is it still reccommended to use powerd to scale the cpu for saving battery on these CPU's? Thanks for the help.

Tomorrow Will Never Die

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