linux-kernel - Re: [PATCH] KVM: VMX: add tracepoint for vpids

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Date:	Tue, 13 Mar 2012 11:58:05 +0100
From:	Davidlohr Bueso <dave@....org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Marcelo Tosatti <mtosatti@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: VMX: add tracepoint for vpids

On Mon, 2012-03-12 at 12:34 +0200, Avi Kivity wrote:
> On 03/12/2012 01:29 PM, Davidlohr Bueso wrote:
> > On Mon, 2012-03-12 at 10:22 +0200, Avi Kivity wrote:
> > > On 03/11/2012 05:57 PM, Davidlohr Bueso wrote:
> > > > From: Davidlohr Bueso <dave@....org>
> > > >
> > > > Add a new tracepoint for vpid allocation and freeing associated to all vCPUs.
> > > >
> > > 
> > > Why?
> > > 
> >
> > We have been using this tracepoint for some time now to help debug vpids
> > and simulating tagged TLB behavior and performance. This gets to be non
> > trivial when working with large amounts of guests and vCPUs.
> 
> I don't follow.  Can you give an example of when this tracepoint would
> be useful?
> 

For example when running lots of guests with many different hardware
configurations (ept on/off, vpid on/off) I trace what vcpu has or
doesn't have a corresponding vpid associated. Perhaps this is more
useful for experimental things than actual KVM development.



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