linux-kernel - Re: [PATCH] x86: add the debugfs interface for the sysprof tool

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Message-Id: <20080223110158.62a3ad6e.akpm@linux-foundation.org>
Date:	Sat, 23 Feb 2008 11:01:58 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Pekka Enberg" <penberg@...helsinki.fi>
Cc:	"Arjan van de Ven" <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, sandmann@...hat.com,
	tglx@...x.de, hpa@...or.com
Subject: Re: [PATCH] x86: add the debugfs interface for the sysprof tool

On Sat, 23 Feb 2008 16:54:49 +0200 "Pekka Enberg" <penberg@...helsinki.fi> wrote:

> On Sat, Feb 23, 2008 at 10:11 AM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> >  Seems a poor idea to me.  Sure, oprofile is "hard to set up", but not if
> >  your distributor already did it for you.
> >
> >  Sidebar: the code uses the utterly crappy register_timer_hook() which
> >
> >  a) is woefully misnamed and
> >
> >  b) is racy and
> >
> >  c) will disrupt oprofile if it is being used.  And vice versa.
> 
> I wonder if sysprof should hook to the same interrupt as oprofile then?

oprofile uses register_timer_hook() for its oh-crap-nothing-else-works
fallback iirc.  It's a useful fallback: I used it a few centuries ago on
some el-cheapo VIA CPU-based thing we had at Digeo.

It's unclear to me whether all this stuff works with NO_HZ=y, btw.  Didn't
we just lose the regular timer interrupts which these clients depend upon?

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