[Xen-devel] Re: expose MWAIT to dom0

To:	"Tian, Kevin" <kevin.tian@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject:	[Xen-devel] Re: expose MWAIT to dom0
From:	Keir Fraser <keir.xen@xxxxxxxxx>
Date:	Mon, 15 Aug 2011 07:54:54 +0100
Cc:	"Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>, "'Keir Fraser \(keir@xxxxxxx\)'" <keir@xxxxxxx>, "Wei, Gang" <gang.wei@xxxxxxxxx>
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On 15/08/2011 06:35, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> Above trick is ugly and error-prone, since it always enable mwait regardless
> of
> actual CPU capability. It's unlikely to make into upstream, and also get lost
> in
> into some distro such as SLES11.
> 
> Instead of enhancing current approach (e.g. add a separate channel to reveal
> mwait capability instead of using cpuid), I'm curious why we don't expose
> mwait
> in cpuid to dom0 directly. At least original comment in 17573 looks obscure,
> since EIST has nothing to do with Cx...

Well the problem is some older kernels will try to use MWAIT if they see the
feature in CPUID. Of course that doesn't work outside ring 0.

 -- Keir



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[Xen-devel] Re: expose MWAIT to dom0