Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

[Waiman Long <longman@xxxxxxxxxx>]

On 09/06/2017 03:08 AM, Peter Zijlstra wrote:
> Guys, please trim email.
>
> On Tue, Sep 05, 2017 at 10:31:46AM -0400, Waiman Long wrote:
>> For clarification, I was actually asking if you consider just adding one
>> more jump label to skip it for Xen/KVM instead of making
>> virt_spin_lock() a pv-op.
> I don't understand. What performance are you worried about. Native will
> now do: "xor rax,rax; jnz some_cold_label" that's fairly trival code.

It is not native that I am talking about. I am worry about VM with
non-Xen/KVM hypervisor where virt_spin_lock() will actually be called.
Now that function will become a callee-saved function call instead of
being inlined into the native slowpath function.

Cheers,
Longman


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