linux-kernel - Re: [PATCH 2/4] ia64: allocate percpu area for cpu0 like percpu areas for other cpus

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Message-ID: <4ABA9B14.20904@kernel.org>
Date:	Thu, 24 Sep 2009 07:03:00 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	Nick Piggin <npiggin@...e.de>, Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	linux-ia64 <linux-ia64@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] ia64: allocate percpu area for cpu0 like percpu areas
 for other cpus

Christoph Lameter wrote:
> On Wed, 23 Sep 2009, Tejun Heo wrote:
> 
>> any special handling.  What problems are you seeing?
> 
> per cpu variable access on IA64 does not use the percpu_offset for the
> calculation of the current per cpu data area. Its using a virtual mapping.
> 
> How does the new percpu allocator support this? Does it use different
> methods of access for static and dynamic percpu access?

That's only when __ia64_per_cpu_var() macro is used in arch code which
always references static perpcu variable in the kernel image which
falls inside PERCPU_PAGE_SIZE.  For everything else, __my_cpu_offset
is defined as __ia64_per_cpu_var(local_per_cpu_offset) and regular
pointer offsetting is used.

Thanks.

-- 
tejun
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