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Re: [Xen-devel] [PATCH] x86 fixes for 3.3 impacting distros (v1).
- To: "Konrad Rzeszutek Wilk" <konrad.wilk@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>
- From: "Jan Beulich" <JBeulich@xxxxxxxx>
- Date: Thu, 28 Jun 2012 16:38:14 +0100
- Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Suresh B Siddha <suresh.b.siddha@xxxxxxxxx>, x86@xxxxxxxxxx, Jason Garrett-Glaser <jason@xxxxxxxx>, marmarek@xxxxxxxxxxxxxxxxxxxxxx, rostedt@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, mingo@xxxxxxxxxx, tglx@xxxxxxxxxxxxx, cyclonusj@xxxxxxxxx
- Delivery-date: Thu, 28 Jun 2012 15:37:38 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
>>> On 28.06.12 at 16:42, "H. Peter Anvin" <hpa@xxxxxxxxx> wrote:
> On 06/28/2012 07:28 AM, Konrad Rzeszutek Wilk wrote:
>> I also chatted with the core Xen hypervisor folks about adding in the
> context switch code
>> to alter the PAT layout - but they were not keen a about it - and I am not
> sure how much
>> CPU cycles one loses by doing a wrmsr to the PAT register on every guest
> context switch
>> (worst case when on has a pvops kernel and a old-style one - where the WC
>> bit
> would differ)?
>>
>
> And you're comparing that to a bunch of new pvops calls? The discussion
> shouldn't even have started until you had ruled out this solution and
> had data to show it.
That's definitely not an option: Xen itself may be (and is, under
certain circumstances at least) using WC page table entries, so
we can't allow on-the-fly changes to the meaning of the various
indexes.
Jan
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