linux-kernel - Re: [patch 02/24] perfmon: base code

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Date:	Thu, 27 Nov 2008 19:41:49 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	eranian@...il.com, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, mingo@...e.hu, x86@...nel.org,
	andi@...stfloor.org, sfr@...b.auug.org.au
Subject: Re: [patch 02/24] perfmon: base code

> 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@...ux.intel.com
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