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

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Date:	Thu, 16 Nov 2006 17:03:50 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Linus Torvalds <torvalds@...l.org>
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, Linus Torvalds wrote:

>  - it makes it clear that this should be fixed, preferably by just having 
>    some way to initialize SRCU structs staticalyl. If we get that, the fix 
>    is to just replace the horrible "initialize by hand" with a static 
>    initializer once and for all.
> 
> Hmm?
> 
> Totally untested, but it compiles and it _looks_ sane. The overhead of the 
> function call should be minimal, once things are initialized.
> 
> 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.  They are a
real mess.  I couldn't think up a way to construct any sort of uniform
interface to per-cpu memory, not without completely changing the guts of 
the per-cpu stuff.

If you or someone else can fix that problem, I will be happy to change the 
SRCU-based notifiers to work both ways.

Alan Stern

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