linux-kernel - Re: [PATCH 1/2] perf: Add persistent event facilities

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Message-ID: <20120518104947.GG20215@aftab.osrc.amd.com>
Date:	Fri, 18 May 2012 12:49:47 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Borislav Petkov <bp@...64.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] perf: Add persistent event facilities

On Fri, May 18, 2012 at 12:09:13PM +0200, Peter Zijlstra wrote:
> On Wed, 2012-03-21 at 15:34 +0100, Borislav Petkov wrote:
> > +                               persistent     :  1, /* always-on event */
> 
> Should creating something like that be privileged?

Yeah, I dunno, do we want that? Well, what it is when we enable an event
during boot, i.e. say "boot_trace=<event>..." on the kernel command line
and this event is enabled until we finish booting. Then we disable it
with perf or over debugfs. Is that privileged or can any user boot-trace
the system?

All good questions.

> And it looks like you allow creating persistent per-task events; is
> that useful, if so why? And like already pointed out, your cleanup
> seems broken in that case.

This was dumb - I wanted to have task-agnostic events which get enabled
for the whole system and there's a buffer on each CPU which collects
their output. It was a first attempt and it is a good thing you gave it
a look so that I can address the issues properly.

Thanks.

-- 
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Boris.

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