From: Kirill A. Korinsky <kirill@korins.ky>
Subject: Re: powersave CPU policy
To: "Lorenz (xha)" <me@xha.li>, OpenBSD tech <tech@openbsd.org>
Date: Wed, 15 May 2024 02:09:07 +0100

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.

-- 
wbr, Kirill