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xen-devel
[Xen-devel] Re: [RFC PATCH V4 5/5] cpuidle: cpuidle driver for apm
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To: |
Trinabh Gupta <trinabh@xxxxxxxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [RFC PATCH V4 5/5] cpuidle: cpuidle driver for apm |
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From: |
Len Brown <lenb@xxxxxxxxxx> |
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Date: |
Wed, 23 Mar 2011 16:32:00 -0400 (EDT) |
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Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>, ak@xxxxxxxxxxxxxxx, suresh.b.siddha@xxxxxxxxx, venki@xxxxxxxxxx, peterz@xxxxxxxxxxxxx, benh@xxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, arjan@xxxxxxxxxxxxxxx |
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Thu, 24 Mar 2011 17:07:14 -0700 |
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Alpine 2.02 (LFD 1266 2009-07-14) |
> > Also wondering why you would ever have a different idle routine on
> > different cpus?
>
> Yes, this is an ongoing debate. Apparently it is a possibility
> because of ACPI bugs. CPU's can have asymmetric C-states
> and overall different idle routines on different cpus. Please
> refer to http://lkml.org/lkml/2009/9/24/132 and
> https://lkml.org/lkml/2011/2/10/37 for a discussion around this.
Althought the ACPI specification allows the BIOS to tell the OS
about different C-states per-processor, I know of zero system
in the field and zero systems in development that require that
capability. That isn't a guarantee that capability will never
be used, but I'm not holding my breath.
If there are systems with broken tables that make them
appear asymetric, then we should have a workaround that handles
that case, rather than complicating the normal code for
the broken case.
So I recommend deleting the extra per-cpu registration stuff
unless there is some other architecture that requires it
and can't hadle the asymmetry in another way.
> I have posted a patch series that does global registration
> i.e same idle routines for each cpu. Please check
> http://lkml.org/lkml/2011/3/22/161 . That series applies on
> top of this series. Global registration significantly
> simplifies the design, but still we are not sure about the
> direction to take.
I'll review that.
thanks,
Len Brown, Intel Open Source Technology Center
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