linux-kernel - Re: [PATCH RFC V9 0/19] Paravirtualized ticket spinlocks

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Message-ID: <20130710104047.GP25631@dyad.programming.kicks-ass.net>
Date:	Wed, 10 Jul 2013 12:40:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Andrew Jones <drjones@...hat.com>, mingo@...hat.com,
	ouyang@...pitt.edu, habanero@...ux.vnet.ibm.com, jeremy@...p.org,
	x86@...nel.org, konrad.wilk@...cle.com, hpa@...or.com,
	pbonzini@...hat.com, linux-doc@...r.kernel.org,
	xen-devel@...ts.xensource.com, mtosatti@...hat.com,
	stefano.stabellini@...citrix.com, andi@...stfloor.org,
	attilio.rao@...rix.com, gregkh@...e.de, agraf@...e.de,
	chegu_vinod@...com, torvalds@...ux-foundation.org,
	avi.kivity@...il.com, tglx@...utronix.de, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, stephan.diestelhorst@....com,
	riel@...hat.com, virtualization@...ts.linux-foundation.org,
	srivatsa.vaddagiri@...il.com
Subject: Re: [PATCH RFC V9 0/19] Paravirtualized ticket spinlocks

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.

> > 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'.

> > 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.
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