From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: KVM PMU virtualization
Date: Fri, 26 Feb 2010 13:47:01 +0200
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References: <4B86917C.4070102@redhat.com> <20100225173423.GB4246@8bytes.org> <20100226084241.GF15885@elte.hu> <4B87987A.2020302@redhat.com> <20100226104437.GB7463@elte.hu> <4B87AD89.60209@redhat.com> <20100226112638.GH7463@elte.hu>
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Cc: Joerg Roedel <joro@8bytes.org>,
	Jes Sorensen <Jes.Sorensen@redhat.com>,
	KVM General <kvm@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Zachary Amsden <zamsden@redhat.com>,
	Gleb Natapov <gleb@redhat.com>, ming.m.lin@intel.com,
	"Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Arjan van de Ven <arjan@infradead.org>,
	Fr??d??ric Weisbecker <fweisbec@gmail.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
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On 02/26/2010 01:26 PM, Ingo Molnar wrote:
>>
>>> By far the biggest instrumentation issue is:
>>>
>>>   - availability
>>>   - usability
>>>   - flexibility
>>>
>>> Exposing the raw hw is a step backwards in many regards.
>>>        
>> In a way, virtualization as a whole is a step backwards.  We take the nice
>> firesystem/timer/network/scheduler APIs, and expose them as raw hardware.
>> The pmu isn't any different.
>>      
> Uhm, it's obviously very different. A fake NE2000 will work on both Intel and
> AMD CPUs. Same for a fake PIT. PMU drivers are fundamentally per CPU vendor
> though.
>
> So there's no "generic hardware" to emulate.
>    

That's true, and it reduces the usability of the feature (you have to 
restrict your migration pools or not expose the pmu), but the general 
points still stand.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.