linux-kernel - Re: comments on Performance Counters for Linux (PCL)

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Message-ID: <20090529085309.GP1065@one.firstfloor.org>
Date:	Fri, 29 May 2009 10:53:09 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andi Kleen <andi@...stfloor.org>, eranian@...il.com,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Robert Richter <robert.richter@....com>,
	Paul Mackerras <paulus@...ba.org>,
	Maynard Johnson <mpjohn@...ibm.com>,
	Carl Love <cel@...ibm.com>,
	Corey J Ashford <cjashfor@...ibm.com>,
	Philip Mucci <mucci@...s.utk.edu>,
	Dan Terpstra <terpstra@...s.utk.edu>,
	perfmon2-devel <perfmon2-devel@...ts.sourceforge.net>
Subject: Re: comments on Performance Counters for Linux (PCL)

> You're talking about VT stuff, right? 

Yes.

> Does that virtualize the PMU too?

A hypervisor can in software, but another common case is a global profiler on 
the host to be able to profile all guests too. e.g. xenoprofile is able to do 
that.

If you want a full system picture with virtualization that's pretty much 
required.

For that you need a concept of more priviledge levels (host user, host sys,
guest user, guest sys)

> Happen to have more details? If they really run in user context their
> priv level would be the same right, otherwise they run in something
> weird, not quite user not quite kernel. Now that might be the case, but
> I'm utterly ignorant on itanic.

See Documentation/ia64/fsys.txt

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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