linux-kernel - Re: [patch] perf_events: even more wrong events for AMD fam10h

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Message-ID: <alpine.DEB.2.00.1106281215530.3859@cl320.eecs.utk.edu>
Date:	Tue, 28 Jun 2011 12:20:44 -0400 (EDT)
From:	Vince Weaver <vweaver1@...s.utk.edu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
cc:	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Robert Richter <robert.richter@....com>,
	Stephane Eranian <eranian@...gle.com>,
	Andre Przywara <andre.przywara@....com>
Subject: Re: [patch] perf_events: even more wrong events for AMD fam10h

On Mon, 27 Jun 2011, Peter Zijlstra wrote:

> On Tue, 2011-06-07 at 17:07 -0400, Vince Weaver wrote:
> > Here are two more problems I found with the superlative "generalized" 
> > events on AMD fam10h.
> > 
> > The "l1-dcache-loads" event measures loads *and* stores.
> >     This might be as close as you can get on AMD, but it's still wrong
> >       as it's not what Intel measures.  
> >     My patch removes it.  Better might be to add a proper
> >     "l1-dcache-access" event.
> 
> The question to ask is, does it still have a strong correlation?

well then shouldn't you call it something like
  "l1-dcache-highly-correlated"
instead?

Having events measure something other than their name is just going to 
confuse users.
 
> > The "l1-dcache-load-miss" event is an invalid event. (0x141).
> >     From what I can tell that event (DATA_CACHE_MISSES) does not
> >     take a mask.  It should be 0x41.  And it's actually measuring
> >     all misses, not just load misses, see above.
> 
> See commit 83112e688f5f05dea1e63787db9a6c16b2887a1d. Also same as above.

that probably warrants a comment in the code.

> > Also, is the value for "no such event" 0 or -1?  The perf_event_amd.c
> > file seems to use them interchangably from what I can tell.
> 
> 	val = hw_cache_event_ids[cache_type][cache_op][cache_result];
> 
> 	if (val == 0)
> 		return -ENOENT;
> 
> 	if (val == -1)
> 		return -EINVAL;

what about architectures where "0" is a valid event?  I know on MIPS 
R12000 "0" means "cycles".

Vince
vweaver1@...s.utk.edu
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