linux-kernel - Re: [RFC][PATCH 2/8] perf, arch: Use early_initcall() for all arch pmu implementations

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Date:	Fri, 26 Nov 2010 16:13:25 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Lin Ming <ming.m.lin@...el.com>,
	Stephane Eranian <eranian@...gle.com>,
	"robert.richter" <robert.richter@....com>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	fweisbec <fweisbec@...il.com>, paulus <paulus@...ba.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Kay Sievers <kay.sievers@...y.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Kyle Moffett <kyle@...fetthome.net>,
	linux-kernel@...r.kernel.org, davem <davem@...emloft.net>,
	Michael Cree <mcree@...on.net.nz>,
	Deng-Cheng Zhu <dengcheng.zhu@...il.com>,
	Will Deacon <will.deacon@....com>,
	Don Zickus <dzickus@...hat.com>,
	Jason Wessel <jason.wessel@...driver.com>
Subject: Re: [RFC][PATCH 2/8] perf, arch: Use early_initcall() for all arch pmu implementations

On Thu, Nov 25, 2010 at 06:55:59PM +0100, Peter Zijlstra wrote:
> On Thu, 2010-11-25 at 11:25 +0100, Peter Zijlstra wrote:
> > 
> > Right, so hw perf init happens from (after this patch):
> > 
> >  arch_initcall: powerpc, arm, sh, mips
> >  early_initcall: x86, sparc, alpha
> > 
> > 
> > Now the problem is that the generic watchdog code (kernel/watchdog.c)
> > tries to create hw perf events, and that too runs from early_initcall.
> > 
> > So my question is, how do we go about curing this, because powerpc, arm,
> > sh and mips are too late and the rest depends on link order to work, not
> > really a nice situation.
> > 
> > There's two categories of solutions:
> >  - move the watchdog later, and
> >  - move the hw perf init earlier.
> > 
> > The former is undesired because we want the watchdog as early as
> > possible, the later needs new infrastructure (also, I don't know if the
> > arch implementations can actually run this early).
> > 
> > So do I create a perf_initcall() or is there another solution that
> > avoids things like calling the watchdog code from all arch init code? 
> 
> So the perf_event_init() site is _waaay_ to early to init stuff.. I
> guess I'll move it all to early_initcall() and I'll move the watchdog to
> an explicit call right after it.
> 
> Something like the below,.. now I guess the question to all of you is,
> can your arch pmu code cope with early_initcall() or does it need to be
> some other place?
> 
Any of the initcall levels are ok for SH at least. The only dependency we
have for the perf code is the clock framework, which comes up during
time_init().
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