linux-kernel - Re: [GIT RFC] percpu: use dynamic percpu allocator as the default percpu allocator

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Message-ID: <20090325141330.2717dc97@skybase>
Date:	Wed, 25 Mar 2009 14:13:30 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, rusty@...tcorp.com.au,
	tglx@...utronix.de, x86@...nel.org, linux-kernel@...r.kernel.org,
	hpa@...or.com, Paul Mundt <lethal@...ux-sh.org>,
	rmk@....linux.org.uk, starvik@...s.com, ralf@...ux-mips.org,
	davem@...emloft.net, cooloney@...nel.org, kyle@...artin.ca,
	matthew@....cx, grundler@...isc-linux.org, takata@...ux-m32r.org,
	benh@...nel.crashing.org, rth@...ddle.net,
	ink@...assic.park.msu.ru, heiko.carstens@...ibm.com
Subject: Re: [GIT RFC] percpu: use dynamic percpu allocator as the default
 percpu allocator

On Wed, 25 Mar 2009 21:27:49 +0900
Tejun Heo <tj@...nel.org> wrote:

> Ingo Molnar wrote:
> > * Tejun Heo <tj@...nel.org> wrote:
> > 
> >>> With your patches and a RELOC_HIDE version that uses the GOTENT 
> >>> indirection the kernel won't compile because the "X" constraint 
> >>> for the GOTENT access needs a symbol and there are quite a few 
> >>> users that pass a pointer. I do not see a simple solution for 
> >>> that problem yet.
> >> Ah... okay.  Now I get it.  It wasn't expecting variables there.  How
> >> about doing the following?
> >>
> >>  #define SHIFT_PERCPU_PTR(ptr, offset) (({				\
> >> 	 if (__builtin_constant_p(ptr))					\
> >> 		 do GOTENT trick;					\
> >> 	 else								\
> >> 		 RELOC_HIDE();						\
> >>  }))
> >>
> >> Thanks.
> > 
> > Btw., is there any intermediate fix/workaround i could apply 
> > perhaps? I'd like to send the percpu bits early in the merge window 
> > and would hate to break Martin's arch ...
> 
> Martin's original patch should do the trick although it would be
> slower for static symbols.  I'll merge it and post the tree.

No, my original patch doesn't work. It will break modules that use
static per-cpu variables.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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