linux-kernel - Re: perf: regression -- missing /sys/devices/system/cpu/perf

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Message-ID: <20110524194810.GB27634@elte.hu>
Date:	Tue, 24 May 2011 21:48:10 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Vince Weaver <vweaver1@...s.utk.edu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, paulus@...ba.org, acme@...hat.com
Subject: Re: perf: regression -- missing /sys/devices/system/cpu/perf_events


* Vince Weaver <vweaver1@...s.utk.edu> wrote:

> On Tue, 24 May 2011, Peter Zijlstra wrote:
> 
> > A much more reliable way is simply doing the syscall and seeing what
> > happens. But if you want to poke around in sysfs, /sys/bus/event_source/
> > is the new location.
> 
> It's been suggested that they can look for the existence of:
>   /proc/sys/kernel/perf_event_paranoid
> 
> is that something not likely to go away?

Well, we indeed do not remove kernel parameters, but checking for that would 
break on systems (or chroot environments) that do not have /proc mounted or 
visible.

So, what is wrong with the method Peter suggested: the presence of the perf 
syscall (it not returning -ENOSYS) is bona fide evidence that perf is 
available.

Thanks,

	Ingo
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