linux-kernel - Re: [PATCH v7 2/3] KVM: x86: trace mmio begin and complete

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Message-ID: <50448F72.80702@redhat.com>
Date:	Mon, 03 Sep 2012 14:07:30 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Dong Hao <haodong@...ux.vnet.ibm.com>
CC:	acme@...radead.org, mtosatti@...hat.com, mingo@...e.hu,
	xiaoguangrong@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH v7 2/3] KVM: x86: trace mmio begin and complete

On 08/27/2012 12:51 PM, Dong Hao wrote:
> From: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> 
> 'perf kvm stat record/report' 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_io_done to trace the time when mmio/pio is
> completed
> 

Why is this so critical?

If a lot of time is spent in in-kernel mmio, then 'perf top' will report
it.  Otherwise the time between kvm_exit and kvm_entry describes the
time spent in the host.  Not all of it is mmio handling, but it is quite
close.

-- 
error compiling committee.c: too many arguments to function
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