On 03/19/2014 06:07 AM, Paolo Bonzini wrote:
Il 19/03/2014 04:15, Waiman Long ha scritto:
You should see the same values with the PV ticketlock. It is not clear
to me if this testing did include that variant of locks?
Yes, PV is fine. But up to this point of the series, we are concerned
about spinlock performance when running on an overcommitted hypervisor
that doesn't support PV spinlocks.
The unfair queue lock is designed in such a way that it will only be
activated when running in a PV guest or it won't be mergeable upstream.
So there must be some way to determine if it is running under a
hypervisor.
Exactly. What you want is boot_cpu_has(X86_FEATURE_HYPERVISOR).
Paolo
The unfair lock is to be enabled by boot time check, not just by the
presence of a configuration macro during the build process in order to
avoid using unfair lock on bare metal. Of course, Linux distros can
modify this if that suits their need.
-Longman
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