linux-kernel - Re: [PATCH 2/3] KVM: improve trace events of vmexit/mmio/ioport

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Message-ID: <20120117115558.GB17420@amt.cnet>
Date:	Tue, 17 Jan 2012 09:55:58 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 2/3] KVM: improve trace events of vmexit/mmio/ioport

On Tue, Jan 17, 2012 at 10:28:11AM +0800, Xiao Guangrong wrote:
> On 01/16/2012 05:38 PM, Avi Kivity wrote:
> 
> > On 01/16/2012 11:32 AM, Xiao Guangrong wrote:
> >> - trace vcpu_id for these events
> > 
> > We can infer the vcpu id from the kvm_entry tracepoints, no?
> > 
> 
> 
> Thanks for your review, Avi!
> 
> Hmm. i think it is hard to do since the vcpu thread can be scheduled
> anytime, one example is as follow:
> 
> CPU 0
> 
> kvm_entry vcpu 0
> ......
> kvm_entry vcpu 1
> ......
> event1 occurs
> ......
> event2 occurs
> 
> It is hard to know the event belong to which kvm_entry?
> 
> >> - add kvm_mmio_done to trace the time when mmio/ioport emulation is completed
> > 
> > ditto?
> > 
> 
> 
> I think is ok to get the event end time by using kvm_entry.
> 
> > 
> > Relying on the existing tracepoints will make the tool work on older
> > kernels.
> > 
> 
> 
> We can drop all new events, but unfortunately, the information of the origin
> tracepoints is not enough, at least vcpu_id need be traced in theses events
> to match its events. Yes?

Yes, and if you don't add completed events, you'll have to use kvm_entry 
whose collection adds a lot of overhead.

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