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

[Igor Mammedov]

On Mon, 23 Mar 2020 13:09:48 +0100
Gerd Hoffmann <address@hidden> wrote:

> On Mon, Mar 23, 2020 at 06:51:10AM -0400, Michael S. Tsirkin wrote:
> > On Thu, Mar 19, 2020 at 09:01:04AM +0100, Gerd Hoffmann wrote:  
> > > I know that not supporting ACPI in microvm is intentional.  If you still
> > > don't want ACPI this is perfectly fine, you can use the usual -no-acpi
> > > switch to toggle ACPI support.
> > > 
> > > These are the advantages you are going to loose then:
> > > 
> > >   (1) virtio-mmio device discovery without command line hacks (tweaking
> > >       the command line is a problem when not using direct kernel boot).
> > >   (2) Better IO-APIC support, we can use IRQ lines 16-23.
> > >   (3) ACPI power button (aka powerdown request) works.
> > >   (4) machine poweroff (aka S5 state) works.  
> > 
> > What is the cost though? How do boot times compare?  
> 
> Well, acpi speeds up booting by one second because this delay ...
> 
>    [    0.275736] i8042: PNP: No PS/2 controller found.
>    [    0.275736] i8042: Probing ports directly.
>    [    1.315447] i8042: No controller found
> 
> ... goes away, at least with standard distro kernels.  When building
> your own you can probably compile out the driver somehow, even though
> something seems to select SERIO_I8042 so trying to simply flip
> CONFIG_SERIO_I8042 to 'n' in .config doesn't work.  And a runtime
> switch seems to not be there either ...
> 
> So that ruined my plan to just time until the root filesystem is
> 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

> So the difference is less than 0.01 seconds on my box.
> 
> cheers,
>   Gerd
>