linux-kernel - Re: [PATCH 1/7] perf: introduce raw_type attribute to specify the type of a raw sample

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Date:	Fri, 21 May 2010 00:46:25 +0200
From:	Robert Richter <robert.richter@....com>
To:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>
Subject: Re: [PATCH 1/7] perf: introduce raw_type attribute to specify the
 type of a raw sample

On 19.05.10 18:02:40, Corey Ashford wrote:

> >  perf record -e r186A:IBS_FETCH ...
> >  perf record -e r0:IBS_FETCH -c 100000 ...
> 
> Should this raw value have been 186A0 instead of 186A?

This is the 20 bit value of the cycle count, but only bits 19:4 are
encoded in bits 15:0 of the raw ibs register. Lower 4 bits of the
cycle count must be null and thus not pushed to the register. The raw
register setup is correct.

> Where is the named type translation coming from?  Is this something
> that needs to be hard-coded into perf?

I was thinking of an enum or macro definition for the values in the
kernel. A name mapping table could be implemented at least in the
userspace, if needed maybe also in the kernel.

> Have you looked at Lin Ming's patch series?  I think it offers
> another way to support IBS and other arch-specific and off-chip PMUs
> in a more general way, though it's not quite fully-baked yet.

Yes, this could be an option too. The proposal was some days ago and a
little hidden in its subject, so I missed it first. But the concept of
registering a pmu feature looks good and could be an alternative to
the raw_value approach.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center
email: robert.richter@....com

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