Re: [Xen-devel] [PATCH 1/3] cpuidle: If disable_cpuidle() is called, set pm_idle to default_idle.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Sun, Nov 13, 2011 at 01:00:15AM -0500, Len Brown wrote:
> > And just found that there is a BZ for this as well:
> > https://bugzilla.redhat.com/show_bug.cgi?id=739499
> >
> > And this patch fixes the Linux kernel to boot under Amazon EC2.
> 
> doesn't matter.
> 
> Working around an Amazon EC2 bug in a newly compiled upstream kernel
> isn't going to help with any of the kernels that don't include that 
> workaround.

Prior to 3.1 we did have a solution for this - we would use the default_idle
and not pick and/choose one based on the CPUID flags.

It was not really a choice made by "hypervisor wrongly advertises the
MWAIT flag", but rather that we want to use the safe_halt, which ends up
calling the yield hypercall.

That is the optimal solution irregardless of what version of hypervisor
is being used.

> 
> Amazon EC2 should not advertise MWAIT support that it does not have,
> and all kernels should run on it w/o any workaround.
> 
> Len Brown, Intel Open Source Technology Center
> 
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