linux-kernel - Re: [PATCH v1 0/5] KVM in-guest performance monitoring

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Message-ID: <4DCBDF5B.6000101@siemens.com>
Date:	Thu, 12 May 2011 15:23:39 +0200
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Joerg Roedel <joro@...tes.org>
CC:	Avi Kivity <avi@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH v1 0/5] KVM in-guest performance monitoring

On 2011-05-12 15:11, Joerg Roedel wrote:
> On Thu, May 12, 2011 at 11:47:51AM +0200, Jan Kiszka wrote:
>> On 2011-05-12 11:33, Joerg Roedel wrote:
> 
>>> Anyway, I thought about a paravirt-approach instead of implementing a
>>> real PMU... But there are certainly good reasons for both.
>>
>> Paravirt is taking away the pressure from CPU vendors to do their virt
>> extensions properly - and doesn't help with unmodifiable OSes.
> 
> Seriously, I think such decisions should be technical only and not
> political like that. The losers of such political decisions are always
> the users because they don't get useful features that are technical
> possible.

Paravirt remains a workaround, useful until hardware provides a solution
for all guests, and that often in an even more efficient way (like for
MMU virtualization).

We do not need to block a PV-PMU for Linux guests (or other OSes that
want to adopt to it), but that will not be a solution for the problem,
that's my point. A PV-PMU may even be useful to demonstrate usefulness
of a virtual PMU the CPU vendors (if they aren't aware of this yet).

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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