linux-kernel - Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall

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Message-ID: <Pine.LNX.4.64.0611161414580.3349@woody.osdl.org>
Date:	Thu, 16 Nov 2006 14:21:57 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Alan Stern <stern@...land.harvard.edu>
cc:	Thomas Gleixner <tglx@...esys.com>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	john stultz <johnstul@...ibm.com>,
	David Miller <davem@...emloft.net>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...l.org>, Andi Kleen <ak@...e.de>,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync

On Thu, 16 Nov 2006, Alan Stern wrote:
> On Thu, 16 Nov 2006, Linus Torvalds wrote:
> >
> > Paul, it would be _really_ nice to have some way to just initialize 
> > that SRCU thing statically. This kind of crud is just crazy.
> 
> I looked into this back when SRCU was first added.  It's essentially 
> impossible to do it, because the per-cpu memory allocation & usage APIs 
> are completely different for the static and the dynamic cases.

I don't think that's how you'd want to do it.

There's no way to do an initialization of a percpu allocation statically. 
That's pretty obvious.

What I'd suggest instead, is to make the allocation dynamic, and make it 
inside the srcu functions (kind of like I did now, but I did it at a 
higher level).

Doing it at the high level was trivial right now, but we may well end up 
hitting this problem again if people start using SRCU more. Right now I 
suspect the cpufreq notifier is the only thing that uses SRCU, and it 
already showed this problem with SRCU initializers.

So I was more thinking about moving my "one special case high level hack" 
down lower, down to the SRCU level, so that we'll never see _more_ of 
those horrible hacks. We'll still have the hacky thing, but at least it 
will be limited to a single place - the SRCU code itself.

		Linus
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