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

[Gleb Natapov <gleb@xxxxxxxxxx>]

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.

> > > 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.

--
                        Gleb.

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