From: Tejun Heo <tj@kernel.org>
To: Christoph Lameter <cl@linux-foundation.org>
Cc: Nick Piggin <npiggin@suse.de>, Tony Luck <tony.luck@intel.com>,
Fenghua Yu <fenghua.yu@intel.com>,
linux-ia64 <linux-ia64@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Rusty Russell <rusty@rustcorp.com.au>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] ia64: allocate percpu area for cpu0 like percpu areas for other cpus
Date: Wed, 23 Sep 2009 11:11:02 +0900 [thread overview]
Message-ID: <4AB983B6.6050203@kernel.org> (raw)
In-Reply-To: <alpine.DEB.1.10.0909221856050.9410@V090114053VZO-1>
Christoph Lameter wrote:
> On Tue, 22 Sep 2009, Tejun Heo wrote:
>
>> +#ifdef CONFIG_SMP
>> + . = ALIGN(PERCPU_PAGE_SIZE);
>> + __cpu0_per_cpu = .;
>
> __per_cpu_start?
>
>> + . = . + PERCPU_PAGE_SIZE; /* cpu0 per-cpu space */
>> +#endif
>
> This is a statically sized per cpu area that is used by __get_cpu_var()
> Data is access via a cpu specific memory mapping. How does this work when
> the area grows beyond PERCPU_PAGE_SIZE? As far as I can see: It seems
> that __get_cpu_var would then cause a memory fault?
On ia64, the first chunk is fixed at PERCPU_PAGE_SIZE. It's something
hardwired into the page fault logic and the linker script. Build will
fail if the static + reserved area goes over PERCPU_PAGE_SIZE and in
that case ia64 will need to update the special case page fault logic
and increase PERCPU_PAGE_SIZE. The area reserved above is interim
per-cpu area for cpu0 which is used between head.S and proper percpu
area setup and will be ditched once initialization is complete.
Thanks.
--
tejun
next prev parent reply other threads:[~2009-09-23 2:11 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-22 7:40 [PATCHSET percpu#for-next] percpu: convert ia64 to dynamic percpu and drop the old one Tejun Heo
2009-09-22 7:40 ` [PATCH 1/4] vmalloc: rename local variables vmalloc_start and vmalloc_end Tejun Heo
2009-09-22 22:52 ` Christoph Lameter
2009-09-23 2:08 ` Tejun Heo
2009-09-22 7:40 ` [PATCH 2/4] ia64: allocate percpu area for cpu0 like percpu areas for other cpus Tejun Heo
2009-09-22 22:59 ` Christoph Lameter
2009-09-23 2:11 ` Tejun Heo [this message]
2009-09-23 13:44 ` Christoph Lameter
2009-09-23 14:01 ` Tejun Heo
2009-09-23 17:17 ` Christoph Lameter
2009-09-23 22:03 ` Tejun Heo
2009-09-24 7:36 ` Christoph Lameter
2009-09-24 8:37 ` Tejun Heo
2009-09-28 15:12 ` Christoph Lameter
2009-09-22 7:40 ` [PATCH 3/4] ia64: convert to dynamic percpu allocator Tejun Heo
2009-09-22 7:40 ` [PATCH 4/4] percpu: kill legacy " Tejun Heo
2009-09-22 8:16 ` [PATCHSET percpu#for-next] percpu: convert ia64 to dynamic percpu and drop the old one Ingo Molnar
2009-09-22 20:49 ` Luck, Tony
2009-09-22 21:10 ` Luck, Tony
2009-09-22 21:24 ` Luck, Tony
2009-09-22 21:50 ` Tejun Heo
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