Re: [PATCH v3 0/6] powerpc: queued spinlocks and rwlocks

[Waiman Long]

On 7/8/20 4:32 AM, Peter Zijlstra wrote:
> On Tue, Jul 07, 2020 at 11:33:45PM -0400, Waiman Long wrote:
> >  From 5d7941a498935fb225b2c7a3108cbf590114c3db Mon Sep 17 00:00:00 2001
> > From: Waiman Long <longman@xxxxxxxxxx>
> > Date: Tue, 7 Jul 2020 22:29:16 -0400
> > Subject: [PATCH 2/9] locking/pvqspinlock: Introduce
> >   CONFIG_PARAVIRT_QSPINLOCKS_LITE
> >
> > Add a new PARAVIRT_QSPINLOCKS_LITE config option that allows
> > architectures to use the PV qspinlock code without the need to use or
> > implement a pv_kick() function, thus eliminating the atomic unlock
> > overhead. The non-atomic queued_spin_unlock() can be used instead.
> > The pv_wait() function will still be needed, but it can be a dummy
> > function.
> >
> > With that option set, the hybrid PV queued/unfair locking code should
> > still be able to make it performant enough in a paravirtualized
> How is this supposed to work? If there is no kick, you have no control
> over who wakes up and fairness goes out the window entirely.
>
> You don't even begin to explain...
I don't have a full understanding of how the PPC hypervisor work myself. 
Apparently, a cpu kick may not be needed.

This is just a test patch to see if it yields better result. It is 
subjected to further modifcation.

Cheers,
Longman