Re: [Xen-devel] [PATCH] x86: Control CR0 TS behavior using dev_na_ts_allowed

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 03/17/2014 01:35 PM, Jan Beulich wrote:
> > > > On 17.03.14 at 13:42, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
> > On Mon, Mar 17, 2014 at 8:38 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
> > > > > > On 17.03.14 at 04:30, Sarah Newman <srn@xxxxxxxxx> wrote:
> > > Not being convinced at all that this is the right approach (in
> > > particular it remains unclear how an affected guest should deal with
> > > running on a hypervisor not supporting the new interface)
> > It looks like the intention of this patch was that if the dom0
> > administrator enables the new option, then it will be on by default,
> > *but* the guest can disable the new behavior.  That way, if an admin
> > knows that she's running all PVOPS kernels (no "classic Xen" kernels),
> > she can enable it system-wide.  Older PVOPS kernels will behave
> > correctly (but a bit slowly), and newer PVOPS kernels will switch to
> > the PVABI behavior and reap the performance benefit.
> >
> > Newer PVOPS kernels running on older hypervisors will simply use the
> > PVABI behavior.
> But if that works correctly, then there's no hypervisor/tools
> change needed in the first place.
Yes, there's still a need to run *old* PVOPS kernels on *new* 
hypervisors.  That (as I understand it) is the point of this patch.
 -George


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