linux-kernel - Re: [patch 04/41] cpu ops: Core piece for generic atomic per cpu operations

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Date:	Tue, 17 Jun 2008 07:21:04 -0700
From:	Mike Travis <travis@....com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Christoph Lameter <clameter@....com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Martin Peschke <mp3@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [patch 04/41] cpu ops: Core piece for generic atomic per cpu
 operations

Rusty Russell wrote:
> On Tuesday 17 June 2008 00:52:08 Christoph Lameter wrote:
>> On Sun, 15 Jun 2008, Rusty Russell wrote:
>>>> 3. Some hooks for arches to override particular behavior as needed.
>>>>    F.e. IA64 allocates percpu structures in a special way. x86_64
>>>>    needs to do some tricks for the pda etc etc.
>>> IA64 is going to need some work, since dynamic percpu addresses won't be
>>> able to use their pinned TLB trick to get the local version.
>> The ia64 hook could simply return the address of percpu area that
>> was reserved when the per node memory layout was generated (which happens
>> very early during node bootstrap).
> 
> Apologies, this time I read the code.  I thought IA64 used the pinned TLB area 
> to access per-cpu vars under some circumstances, but they only do that via an 
> arch-specific macro.
> 
> So creating new congruent mappings to expand the percpu area(s) is our main 
> concern now?
> 
> Rusty.

Not exactly.  Getting the system to not panic early in the boot (before
x86_64_start_kernel()) is the primary problem right now.  This happens
in the tip tree with the change to use zero-based percpu offsets.  It
gets much farther on the linux-next tree.

Thanks,
Mike
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