Date: Thu, 27 Nov 2008 19:41:49 +0100
From: Andi Kleen <andi@firstfloor.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: eranian@gmail.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
       mingo@elte.hu, x86@kernel.org, andi@firstfloor.org,
       sfr@canb.auug.org.au
Subject: Re: [patch 02/24] perfmon: base code
Message-ID: <20081127184149.GR6703@one.firstfloor.org>
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> Well, where is it checked ? Where is checked whether Oprofile runs or not ?

That is done using the perfctr reservation. I saw that somewhere in the
patchkit. The NMI watchdog uses that too.

> > The Oprofile reservation you see is built on top of the cpumask reservation.
> > It tries to allocate in one call and atomically ALL the CPUs as this is the way
> > Oprofile operates. Thus it fails if one perfmon system-wide session or one
> > perfmon per-thread exists.
> 
> This only prevents oprofile from starting, but it does neither prevent
> thread sessions nor does it prevent a perfmon per cpu session on a cpu
> which was onlined after oprofile started, simply because it's bit is
> missing in the CPU mask. 

The perfctr reservation is global over all CPUs.

-Andi 

-- 
ak@linux.intel.com
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