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Re: [PATCH 00/13] microvm: add acpi support


From: Igor Mammedov
Subject: Re: [PATCH 00/13] microvm: add acpi support
Date: Wed, 25 Mar 2020 10:53:00 +0100

On Wed, 25 Mar 2020 10:16:36 +0100
Gerd Hoffmann <address@hidden> wrote:

> > > mounted.  Decided to use the "i8042: PNP: No PS/2 controller found."
> > > line instead for a simple test (just check the kernel log timestamps,
> > > three runs each).  The ACPI initialization is already done at that
> > > point, so it should be useful nevertheless.  Here we go:
> > > 
> > > Without acpi:
> > >   0.277710
> > >   0.278852
> > >   0.279520
> > > 
> > > With acpi:
> > >   0.283917
> > >   0.284262
> > >   0.284836  
> > I wonder what would be difference with hw-reduced acpi  
> 
> The kernel does a bunch of reads+writes at boot (roughly 20-30),
> mostly timer ports, so probably while initializing the pm_timer
> clocksource.  Then it stops talking to the acpi hardware,
> preferring kvmclock clocksouce I guess.
> 
> So I expect hw-reduced acpi wouldn't make much of a difference.
> Actually trying that isn't that high on my priority list.

there aren't pm timers on hw-reduced, that's the point of it
(a bunch of registers that where mandatory with full profile
are absent so OS doesn't have to initialize not needed stuff)

> There is bigger fish to fry, untangling the hw/i386/acpi-build.c
> monster for starters, so building with ACPI=y + PCI=n works ...
> 
> cheers,
>   Gerd
> 




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