linux-kernel - Re: [PATCH v2 2/3] KVM: x86: add tracepoints to trace mmio begin and complete

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Date:	Fri, 03 Feb 2012 01:55:16 +0800
From:	Xiao Guangrong <xiaoguangrong.eric@...il.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Stefan Hajnoczi <stefanha@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] KVM: x86: add tracepoints to trace mmio begin
 and complete

On 02/03/2012 01:36 AM, Avi Kivity wrote:

> On 02/02/2012 07:27 PM, Xiao Guangrong wrote:
>> From: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
>>
>> 'perf kvm-events' will use kvm_exit and kvm_mmio(read...) to calculate
>> mmio read emulated time for the old kernel, in order to trace mmio read
>> event more exactly, we add kvm_mmio_begin to trace the time when mmio read
>> begins
>>
>> Also, add kvm_mmio_done to trace the time when mmio/pio is completed
> 
> Previously, we discussed using the kvm_entry to do this.  This reduces
> the number of tracepoints, and is backwards compatible.  What was the
> conclusion?
> 


Since using kvm_entry can cause lots of unnecessary calculated, these new two
tracepoints can let the result be exacter.

And, they are only used in new kernel, we will fall back to using kvm_entry if
they are not existing, that means it does not break backwards compatible.
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