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

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Date:	Wed, 25 Mar 2009 00:22:44 +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

Tejun Heo wrote:
> 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.

Ping.

-- 
tejun
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