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

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Message-ID: <49C300D8.5080204@kernel.org>
Date:	Fri, 20 Mar 2009 11:35:04 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
CC:	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

Hello, Martin.

Sorry about the delay.

Martin Schwidefsky wrote:
> We do have a problem with #2, the dynamic percpu patches currently
> breaks s390. But the nice thing is that we can now get rid of the GOTENT
> relocation for the percpu symbols. If the code is changed to use
> RELOC_HIDE for the SHIFT_PERCPU_PTR define, everything works just fine.
> Patch attached. Nice works guys.
> 
> Subject: [PATCH] s390: percpu access.
> 
> From: Martin Schwidefsky <schwidefsky@...ibm.com>
> 
> With the dynamic percpu allocator there is no need anymore to play
> tricks with the GOTENT relocation for the access to the percpu
> symbols. A simple RELOC_HIDE gets the job done.

Hmm... I don't quite get it.  The GOTENT was to work around large
offsets for modules, right?  Can you please explain what changed by
the dynamic percpu allocator?

> +#define SHIFT_PERCPU_PTR(var, offset) RELOC_HIDE(&per_cpu_var(var), (offset))

Hmm... @var already has per_cpu__ prefix when the above macro is
invoked, so doing per_cpu_var() on it again wouldn't work.  If simple
RELOC_HIDE works, you should be able to simply drop the above
definition.  The generic percpu.h will define it.

Thanks.

-- 
tejun
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