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

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Date:	Thu, 02 Apr 2009 10:54:04 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
CC:	David Miller <davem@...emloft.net>, mingo@...e.hu,
	rusty@...tcorp.com.au, tglx@...utronix.de, x86@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com, lethal@...ux-sh.org,
	rmk@....linux.org.uk, starvik@...s.com, ralf@...ux-mips.org,
	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 Schwidefsky wrote:
>> Also, there is no guarantee that the offset from dynamic allocator
>> will fall in the same 4G.  There is reserve mechanism for static ones
>> for archs which need it but for dynamic ones, the offset can be any
>> value.
> 
> If we map the modules with a 4GB distance to the main kernel image then
> we don't have to worry about the offsets anymore. The compiler could
> just use LARL to get the address of the static per-cpu variables and
> SHIFT_PERCPU_PTR could be a RELOC_HIDE.

Ah... okay.  Great.  No more GOTENT trick for static ones and for
dynamic ones the compiler will generate indirection.

> It just that the remapping we need to do is sooo icky ..

Fingers and toes crossed.  It would improve general percpu access
performance too.

Thanks.

-- 
tejun
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