linux-kernel - Re: [PATCH RFC 0/5] hard_smp_processor

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Message-Id: <1172805046.3362.20.camel@sebastian.intellilink.co.jp>
Date:	Fri, 02 Mar 2007 12:10:46 +0900
From:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	fastboot@...ts.osdl.org, ebiederm@...ssion.com, ak@...e.de,
	akpm@...ux-foundation.org, judith@...ux-foundation.org
Subject: Re: [PATCH RFC 0/5] hard_smp_processor_id overhaul

On Thu, 2007-03-01 at 09:06 -0500, Benjamin LaHaise wrote:
> On Thu, Mar 01, 2007 at 04:16:13PM +0900, Fernando Luis Vázquez Cao wrote:
> > As a consequence, the hardcoding of hard_smp_processor_id() to 0 on UP
> > systems (see "linux/smp.h") is not correct.
> > 
> > This patch-set does the following:
> > 
> > 1- Remove hardcoding of hard_smp_processor_id on UP systems.
> 
> NAK.  This has to be configurable, as many embedded systems don't even 
> have APICs.  Please rework the patch set so that there is not any overhead 
> for existing UP systems.
In i386 (with the exception of voyager) and x86_64,
hard_smp_processor_id is not used anywhere in the kernel when there are
no APICs available.

Regarding the overhead, hard_smp_processor_id is used mostly during
initialization and doesn't seem to be used in any fast path in i386,
x86_64, and ia64. All the other architectures are not affected by this
patch, because I kept the hardcoding of hard_smp_processor_id on UP
kernels, and just moved the definition to asm/smp.h because it should be
handled by architecture-speficic code.

So unless strictly necessary I would not like to make this patches
dependent on kdump.

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