From: "Theo de Raadt" <deraadt@openbsd.org>
Subject: Re: powersave CPU policy
To: "Lorenz (xha)" <me@xha.li>, OpenBSD tech <tech@openbsd.org>
Date: Tue, 14 May 2024 19:14:16 -0600

Kirill A. Korinsky <kirill@korins.ky> wrote:

> On Wed, 15 May 2024 00:53:37 +0100,
> "Theo de Raadt" <deraadt@openbsd.org> wrote:
> > 
> > > This patch dynamically removes CPU cores when the system is idle to prevent
> > > the scheduler from using them for any task, i.e. assuming the hardware puts
> > > unused CPU to sleep to save some power.
> > 
> > I am pretty sure that assumption is incorrect.  There is some logic for
> > choosing Cx states for cpus, but I very much doubt that a deep-sleep mode
> > is chosen.
> > 
> 
> It depends on the supported method to idle at acpicpu. The code achieves
> that CPU goes to idle via acpicpu_idle, which does MWAIT or HALT for the
> best available (supported?) C-state.

Actually, in a seperate conversation I've had, it isn't choosing the best
state *for this*.  It looks like it always chooses a come-back-quickly state.