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

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Message-ID: <20090529065104.GO1065@one.firstfloor.org>
Date:	Fri, 29 May 2009 08:51:04 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	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>,
	Andi Kleen <andi@...stfloor.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)

> >        Take Itanium, it has 4 priv levels and the PMU counters can monitor at
> >        any priv levels or combination thereof?
> 
> x86 has more priv rings too, but linux only uses 2, kernel (ring 0) and
> user (ring 2 iirc). Does ia64 expose more than 2 priv levels in linux?

In a hardware virtualized environment x86 Linux uses at least four.

And yes ia64 also exposes more I believe, e.g. it has the fancy
"system calls that run in user context"

-Andi

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