linux-kernel - Re: [PATCH 3/4] x86_64: Fold pda into per cpu area

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Date:	Sat, 16 Feb 2008 22:22:17 -0800
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	travis@....com, "Andrew Morton" <akpm@...ux-foundation.org>,
	"Andi Kleen" <ak@...e.de>, "Thomas Gleixner" <tglx@...utronix.de>,
	"Jeremy Fitzhardinge" <jeremy@...p.org>,
	"Christoph Lameter" <clameter@....com>,
	"Jack Steiner" <steiner@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] x86_64: Fold pda into per cpu area

On Feb 15, 2008 12:16 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * travis@....com <travis@....com> wrote:
>
> >  include/asm-generic/vmlinux.lds.h |    2 +
> >  include/linux/percpu.h            |    9 ++++-
>
> couldnt these two generic bits be done separately (perhaps a preparatory
> but otherwise NOP patch pushed upstream straight away) to make
> subsequent patches only touch x86 architecture files?

this patch need to apply to mainline asap.

or you need revert to the patch about include/asm-x86/percpu.h

+#ifdef CONFIG_X86_64
+#include <linux/compiler.h>
+
+/* Same as asm-generic/percpu.h, except that we store the per cpu offset
+   in the PDA. Longer term the PDA and every per cpu variable
+   should be just put into a single section and referenced directly
+   from %gs */
+
+#ifdef CONFIG_SMP
+#include <asm/pda.h>
+
+#define __per_cpu_offset(cpu) (cpu_pda(cpu)->data_offset)
+#define __my_cpu_offset read_pda(data_offset)
+
+#define per_cpu_offset(x) (__per_cpu_offset(x))
+
 #endif
+#include <asm-generic/percpu.h>
+
+DECLARE_PER_CPU(struct x8664_pda, pda);
+
+#else /* CONFIG_X86_64 */

because current tree
in setup_per_cpu_areas will have
     cpu_pda(i)->data_offset = ptr - __per_cpu_start;

but at that time all APs will use cpu_pda for boot cpu...,and APs will
get their pda in do_boot_cpu()

the result is all cpu will have same data_offset, there will share one
per_cpu_data..that is totally wrong!!

that could explain a lot of strange panic ....recently about NUMA...

YH
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