linux-kernel - perf rapl/powercap : powercap has more lenient permissions

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Date:	Wed, 24 Feb 2016 11:42:06 -0500 (EST)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: perf rapl/powercap : powercap has more lenient permissions

Hello

so perf_event requires paranoid value of 0 to read the RAPL counters

	perf stat -a -e power/energy-cores/ /bin/ls
Error:
You may not have permission to collect system-wide stats.

But I can use the new powercap driver to read the same values no problem:

	cat /sys/devices/virtual/powercap/intel-rapl/intel-rapl:0/intel-rapl:0:0/energy_uj
121384969344

Is this expected?  Should the powercap permissions be locked down more?	

Just hitting this, as PAPI has at least 4 different interfaces to read the 
RAPL power values (perf_event, /dev/msr, libmsr, powercap).  Five if you 
count that AMD exports their equivelent info via the hwmon interface.

Vince