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

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.


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