Re: [RESEND] ACPI / processor_idle: use dead loop instead of io port access for wait

[Yin, Fengwei]

On 10/14/2019 5:38 PM, Rafael J. Wysocki wrote:
> On Friday, October 11, 2019 3:30:41 PM CEST Yin, Fengwei wrote:
> > On 10/11/2019 5:05 PM, Rafael J. Wysocki wrote:
> > > Sorry for the delay.
> > No problem.
> >
> > > On Monday, September 9, 2019 9:39:37 AM CEST Yin Fengwei wrote:
> > > > In function acpi_idle_do_entry(), we do an io port access to guarantee
> > > > hardware behavior. But it could trigger unnecessary vmexit for
> > > > virtualization environemnt.
> > >
> > > Is this a theoretical problem, or do you actually see it?
> > >
> > > If you see it, I'd like to have a pointer to a bug report regarding it
> > > or similar.
> > We did see this issue when we run linux as guest with ACRN hypervisor
> > instead of kvm or xen. In our case, we export all native C states to
> > guest and let guest choose which C state it will enter.
> >
> > And we observed many pm timer port access when guest tried to enter
> > deeper C state (Yes, we emulate pm timer so pm timer access will trigger
> > vmexit).
>
> Can you please put this information into the changelog of your patch?
I added this information to the patch commit message and sent out v2.
Thanks a lot for reviewing and comments.

Regards
Yin, Fengwei

> It works very well as a rationale for me. :-)