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Re: [Xen-devel] fpu_taskswitch adjustment proposal
- To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>
- From: Keir Fraser <keir@xxxxxxx>
- Date: Mon, 18 Jun 2012 23:35:43 +0100
- Cc: xen-devel <xen-devel@xxxxxxxxxxxxx>
- Delivery-date: Mon, 18 Jun 2012 22:36:24 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xen.org>
- Thread-index: Ac1NorIASNJZUgrjfkCgkFXGWYarrg==
- Thread-topic: [Xen-devel] fpu_taskswitch adjustment proposal
On 18/06/2012 19:24, "Konrad Rzeszutek Wilk" <konrad.wilk@xxxxxxxxxx> wrote:
>>> It should be possible for the guest kernel to track its CR0.TS setting
>>> shouldn't it? It gets modified only via a few paravirt hooks, and implicitly
>
> Hm, the clts() paravirt could take advantage of the per-cpu cr0 to
> figure out whether it truly needs to do anything.
Exactly.
>>> cleared on #NM.
>> Sure, but selling this to the Linux maintainers I would expect to be
>> harder than fitting the Xen side of things into the current save-
>> and-restore model the native xor code uses. It would only be strait
>> forward to implement on the legacy, forward ported trees.
>>
>> However, with the #NM handler in pv-ops apparently not
>> leveraging the fact that CR0.TS is already cleared for it on entry,
>> maybe this could indeed be introduced together. Konrad?
>
> Would this require an extra pvops call from the #NM handler?
Or we wrap the #NM handler (somehow?) and clear the per-cpu cr0.ts software
flag before calling into the generic #NM handler.
-- Keir
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