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

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Date:	Tue, 24 May 2011 23:37:35 +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, Ingo Molnar wrote:
> > 
> > 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.
> 
> it's just hard to do that from a shell script.

Yeah.

> also, running the perf syscall can be tricky if you have a new kernel but an 
> older set of header files that doesn't have the syscall number defined.

I suspect you could add some quick band-aid like:

#ifndef __NR_perf_event_open
# ifdef __i386__
#  define __NR_perf_event_open 336
# endif
# ifdef __x86_64__ 
#  define __NR_perf_event_open 298
# endif
# ifdef __powerpc__
#  define __NR_perf_event_open 319
# endif
# ifdef __arm__
#  define __NR_perf_event_open 364
# endif
#endif

#ifndef __NR_perf_event_open
# error Please add the __NR_perf_event_open definition for this architecture!
#endif

This should cover 99% of the users - and fill in the table as people report 
build failures :)

Thanks,

	Ingo
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