linux-kernel - Re: [PATCHv2 00/14] perf diff: Factor diff command

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Message-ID: <20121002163002.GD16230@one.firstfloor.org>
Date:	Tue, 2 Oct 2012 18:30:02 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCHv2 00/14] perf diff: Factor diff command

> > Some minor issues I ran into (but no show stoppers):
> > - The error messages for bad -c expressions could be better
> > - I found the requirement for no space after -c unintuitive.
> 
> I'll see to that > 
> > - It would be nice to have support for doing the bucketizing per line
> > instead of per function. With a large function and/or inlining 
> > it's sometimes hard to identify the actual problem
> > Acme recently added this for perf report.
> 
> hm, I missed this one.. hopefully it should be no problem to add it

Here's more issues I found (again no show stopper):

For example you have a spinlock problem with different spinlock callers
that you want to handle.  Since the spinlocks are own functions which
are mixed together cannot be easily ratiod.

This is probably a bit hard to handle, but one way would be to use
a variant of the inclusive reporting Arun recently submitted. 
Define groups of callers that have a combined cost including all 
callees. Use this as the diff unit.

I really liked the oprofile behaviour of attributing lock costs 
to the caller by default. With that it would just work.

The other problem I ran into is that perf archive doesn't seem to 
work very well with kernels, so it's hard to move profiles from
different kernels around to diff them (e.g. for a performance regression)
One way around this would be options to diff to specify the vmlinux etc.
manually

-Andi
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