linux-kernel - Re: [RFC PATCH 3/3 v2] perf: Update perf tool to monitor uncore events

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Date:	Sun, 21 Nov 2010 13:09:35 +0100
From:	"Andi Kleen" <andi@...stfloor.org>
To:	"Lin Ming" <ming.m.lin@...el.com>
Cc:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Stephane Eranian" <eranian@...gle.com>,
	"Andi Kleen" <andi@...stfloor.org>,
	"lkml" <linux-kernel@...r.kernel.org>,
	"Frederic Weisbecker" <fweisbec@...il.com>,
	"Arjan van de Ven" <arjan@...radead.org>
Subject: Re: [RFC PATCH 3/3 v2] perf: Update perf tool to monitor uncore
 events

>
>              samples  pcnt function               DSO
>              _______ _____ ______________________
> ____________________________________
>
>                 8.00 18.6% kallsyms_expand_symbol [kernel.kallsyms]

Reporting a symbol for an uncore event seems highly misleading.
After all the uncore counter has no idea for which core the event was,
so there isn't really any instruction pointer to report.
The event could be event caused by a PCI device or similar.

For per function monitoring of uncore events one has to use
OFFCORE_RESPONSE, like I implemented recently.

I would suggest to not report any symbol names for uncore events.
Doing so just will confuse users.

In fact I suspect uncore events are only really useful
with "stat", but not with "top", or if they are used in top
then the symbol reporting should be disabled.

-Andi

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