linux-kernel - Re: [RFC] [PATCH 1/1] perf: add support for arch-dependent symbolic event names to "perf stat"

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Message-ID: <20100311191441.GA7593@elte.hu>
Date:	Thu, 11 Mar 2010 20:14:41 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC] [PATCH 1/1] perf: add support for arch-dependent symbolic
 event names to "perf stat"


* Corey Ashford <cjashfor@...ux.vnet.ibm.com> wrote:

> On 3/11/2010 4:46 AM, Ingo Molnar wrote:
> [snip]
> >If you want extensible events you can already do it by providing an ftrace
> >tracepoint event via TRACE_EVENT. They are easy to add and ad-hoc, and are
> >supported throughout by perf.
> 
> Is TRACE_EVENT an appropriate way to add hardware-specific counter
> events?  I will look into this.  Thanks for the pointer.
> 
> >
> >That could be librarized further by providing an /eventfs or /proc/events
> >interface to enumerate them.
> 
> We can enumerate events this way, but there are other aspects to
> events than just their names (see below).
> 
> >
> >Or if you want to extend the perf events namespace ABI you can send patches
> >for that as well. (It's not a big issue if a particular event is currently
> >only supported on Power for example - as long as you make a good effort naming
> >and structuring it in a reasonably generic way.)
> 
> I'm not sure how that would work.  The issue I am trying to solve
> here is that Power arch chips have a large number of very
> hardware-specific events that are not generalizable.  Many of these
> events not only have names, but other user-configurable bits as well
> that select or narrow the scope of which exact events are recorded.
> This issue is dealt with nicely in libpfm4, as it has mechanisms for
> parsing event names and attributes (aka modifiers or unit masks),
> and then produces a usable config field for the perf_events_attr
> struct.
> 
> Should I take it from the above that you are completely against the
> idea of using an external library for hardware-specific event and
> attribute naming?

Could you give a few relevant examples of events in question, and the kind of 
configurability/attributes they have on Power?

Thanks,

	Ingo
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