Re: [PATCH v2] powerpc ticket locks

On Tue, 2014-02-11 at 11:40 +0100, Torsten Duwe wrote:

On Tue, Feb 11, 2014 at 03:23:51PM +0530, Raghavendra KT wrote:

quoted

How much important to have holder information for PPC? From my
previous experiment
on x86, it was lock-waiter preemption which is problematic rather than
lock-holder preemption.

It's something very special to IBM pSeries: the hypervisor can assign
fractions of physical CPUs to guests. Sometimes a guest with 4 quarter
CPUs will be faster than 1 monoprocessor. (correct me if I'm wrong).

The directed yield resolves the silly situation when holder and waiter
reside on the same physical CPU, as I understand it.

x86 has nothing comparable.

How is this different from the very ordinary case of an SMP KVM guest
whose vcpus are not bound to host cpus, and thus you could have multiple
vcpus running on the same host cpu?

-Scott