linux-kernel - Re: [Q] perf, x86: should perf_event

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Message-ID: <20100529131931.GI5322@lenovo>
Date:	Sat, 29 May 2010 17:19:31 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Q] perf, x86: should perf_event_x.c being compiled
	conditionally?

On Sat, May 29, 2010 at 05:02:54PM +0400, Cyrill Gorcunov wrote:
> On Sat, May 29, 2010 at 09:38:57AM +0200, Peter Zijlstra wrote:
> > On Sat, 2010-05-29 at 01:35 +0400, Cyrill Gorcunov wrote:
> > > Hi,
> > > 
> > > while was building the kernel for pretty old laptop I've noticed
> > > that perf_event_x.c depends on CONFIG_CPU_SUP_ only. So I'm somehow
> > > confused. Should not some additional condition being used?
> > > 
> > > For example if a person have Core 2 or Nehalem machine, he will
> > > definitely not need p6 and p4 events (yes, they are not _that_ big
> > > in size, but anyway).
> > > 
> > > On the other hands distro builders would prefer to have all compiled in.
> > > 
> > > Not sure about what is the best way to resolve this, but perhaps I'm just
> > > missing some key moment?
> > 
> > We had to split out on the CPU_SUP_* stuff because the AMD support
> > relies on symbols otherwise not present.
> > 
> > So fixing build dependencies is the main reason we have that.
> > 
> > If you want to extend it, feel free, but be sure to test the
> > full .config space ;-)
> > 
> 
> Thanks for explanation. I guess we may have something like below.
> Note that I didn't squeeze into *.c files, only Kconfig is touched
> so that we get "Processor type and features" -> "Supported Perfomance
> Events" menu. All entries are "Y" by default and depends on
> PERF_EVENTS && CPU_SUP_INTEL (since we have this trick for Intel
> cpus only at moment). Just an idea.
> 

I'll take a more closer look (since we will need some placeholders
for unconditionally called funtions).

	-- Cyrill
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