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From: ebiederm@xmission.com (Eric W. Biederman)
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@elte.hu>, Andi Kleen <andi@firstfloor.org>,
	lkml - Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/4] i386 GDT cleanups: Use per-cpu GDT immediately upon boot
Date: Wed, 21 Mar 2007 03:31:03 -0600	[thread overview]
Message-ID: <m1aby7c59k.fsf@ebiederm.dsl.xmission.com> (raw)
In-Reply-To: <1174458938.11680.150.camel@localhost.localdomain> (Rusty Russell's message of "Wed, 21 Mar 2007 17:35:38 +1100")

Rusty Russell <rusty@rustcorp.com.au> writes:

> Now we are no longer dynamically allocating the GDT, we don't need the
> "cpu_gdt_table" at all: we can switch straight from "boot_gdt_table"
> to the per-cpu GDT.  This means initializing the cpu_gdt array in C.
>
> The boot CPU uses the per-cpu var directly, then in smp_prepare_cpus()
> it switches to the per-cpu copy just allocated.  For secondary CPUs,
> the early_gdt_descr is set to point directly to their per-cpu copy.
>
> For UP the code is very simple: it keeps using the "per-cpu" GDT as
> per SMP, but we never have to move.

> diff -r a8a4e2f9da08 arch/i386/kernel/head.S
> --- a/arch/i386/kernel/head.S	Wed Mar 21 15:20:48 2007 +1100
> +++ b/arch/i386/kernel/head.S	Wed Mar 21 15:32:38 2007 +1100
> @@ -599,67 +599,10 @@ idt_descr:
>  	.word 0				# 32 bit align gdt_desc.address
>  ENTRY(early_gdt_descr)
>  	.word GDT_ENTRIES*8-1
> -	.long cpu_gdt_table
> -
> -/*
> - * The boot_gdt_table must mirror the equivalent in setup.S and is
> - * used only for booting.
> - */

It looks like you are killing a useful comment here for no good reason.

> +	.long per_cpu__cpu_gdt		/* Overwritten for secondary CPUs */
> +
>  	.align L1_CACHE_BYTES
>  ENTRY(boot_gdt_table)
>  	.fill GDT_ENTRY_BOOT_CS,8,0
>  	.quad 0x00cf9a000000ffff	/* kernel 4GB code at 0x00000000 */
>  	.quad 0x00cf92000000ffff	/* kernel 4GB data at 0x00000000 */


Eric

  parent reply	other threads:[~2007-03-21  9:31 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-03-21  6:10 [PATCH] Allow per-cpu variables to be page-aligned Rusty Russell
2007-03-21  6:30 ` [PATCH 0/4] i386 GDT cleanups Rusty Russell
2007-03-21  6:32   ` [PATCH 1/4] i386 GDT cleanups: Use per-cpu variables for GDT, PDA Rusty Russell
2007-03-21  6:35     ` [PATCH 2/4] i386 GDT cleanups: Use per-cpu GDT immediately upon boot Rusty Russell
2007-03-21  6:36       ` [PATCH 3/4] i386 GDT cleanups: clean up cpu_init() Rusty Russell
2007-03-21  6:53         ` [PATCH 4/4] i386 GDT cleanups: cleanup GDT Access Rusty Russell
2007-03-21  9:31       ` Eric W. Biederman [this message]
2007-03-21 11:55         ` [PATCH 2/4] i386 GDT cleanups: Use per-cpu GDT immediately upon boot Rusty Russell
2007-03-21 16:51           ` Eric W. Biederman
2007-03-21 23:58             ` Rusty Russell
2007-03-22  8:10               ` Sébastien Dugué
2007-03-22  9:24                 ` Rusty Russell
2007-03-22 15:59                   ` [PATCH] i386 GDT cleanups: Rename boot_gdt_table to boot_gdt Sébastien Dugué
2007-03-23  7:19                     ` Rusty Russell
2007-03-23 14:15                     ` Andi Kleen
2007-03-21  9:21 ` [PATCH] Allow per-cpu variables to be page-aligned Eric W. Biederman
2007-03-21 11:44   ` Rusty Russell
2007-03-21 16:49     ` Eric W. Biederman
2007-03-22  0:09       ` Rusty Russell

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