linux-kernel - Use case for PERF_COUNT_HW_REF_CPU

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Message-ID: <4F3243D4.4080907@linux.vnet.ibm.com>
Date:	Wed, 08 Feb 2012 15:13:48 +0530
From:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu
Subject: Use case for PERF_COUNT_HW_REF_CPU_CYCLES generic PMU event

Hello Stephane, 

I was going through the following discussion where we added the
new HW generic event PERF_COUNT_HW_REF_CPU_CYCLES.

https://lkml.org/lkml/2011/12/10/103 

(Sorry, for asking this question bit late)

I am trying to understand the use case for this. Would this new event
help us in generating (during a perf session) a CPU frequency invariant
time metric against which we would plot our other perf event's measurements ?
CPU frequency independent time measurement is it's primary purpose ? or we were
finding a way to expose the fixed counter 2 which was not getting used before 
for not having an event encoding. I guess this would help us in finding equivalent
PMU events or mechanisms in other architecture / platforms.

-- 
Anshuman Khandual
Linux Technology Centre
IBM Systems and Technology Group

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