Re: [Xen-devel] [PATCH RFC V9 0/19] Paravirtualized ticket spinlocks

[Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>]

On 07/10/2013 04:17 PM, Gleb Natapov wrote:
> On Wed, Jul 10, 2013 at 12:40:47PM +0200, Peter Zijlstra wrote:
> > On Wed, Jul 10, 2013 at 01:33:25PM +0300, Gleb Natapov wrote:
> >
> > Here's an idea, trim the damn email ;-) -- not only directed at gleb.
> Good idea.
>
> > > > Ingo, Gleb,
> > > >
> > > >  From the results perspective, Andrew Theurer, Vinod's test results are
> > > > pro-pvspinlock.
> > > > Could you please help me to know what will make it a mergeable
> > > > candidate?.
> > > I need to spend more time reviewing it :) The problem with PV interfaces
> > > is that they are easy to add but hard to get rid of if better solution
> > > (HW or otherwise) appears.
> > How so? Just make sure the registration for the PV interface is optional; that
> > is, allow it to fail. A guest that fails the PV setup will either have to try
> > another PV interface or fall back to 'native'.
> We have to carry PV around for live migration purposes. PV interface
> cannot disappear under a running guest.
IIRC, The only requirement was running state of the vcpu to be retained.
This was addressed by
[PATCH RFC V10 13/18] kvm : Fold pv_unhalt flag into GET_MP_STATE ioctl 
to aid migration.
I would have to know more if I missed something here.

> > > > I agree that Jiannan's Preemptable Lock idea is promising and we could
> > > > evaluate that  approach, and make the best one get into kernel and also
> > > > will carry on discussion with Jiannan to improve that patch.
> > > That would be great. The work is stalled from what I can tell.
> > I absolutely hated that stuff because it wrecked the native code.
> Yes, the idea was to hide it from native code behind PV hooks.

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