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

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Date:	Mon, 14 Nov 2011 09:37:16 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Len Brown <lenb@...nel.org>
Cc:	len.brown@...el.com, jeremy@...p.org,
	xen-devel@...ts.xensource.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, stable@...nel.org, mingo@...hat.com,
	bp@...en8.de, hpa@...or.com, tj@...nel.org, tglx@...utronix.de,
	trenn@...e.de
Subject: Re: [Xen-devel] [PATCH 1/3] cpuidle: If disable_cpuidle() is called,
 set pm_idle to default_idle.

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
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xensource.com
> http://lists.xensource.com/xen-devel
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