linux-kernel - Re: [PATCH 00/10] x86, xsave: some code cleanups and reworks

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Message-ID: <20100720194606.GO26154@erda.amd.com>
Date:	Tue, 20 Jul 2010 21:46:06 +0200
From:	Robert Richter <robert.richter@....com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 00/10] x86, xsave: some code cleanups and reworks

On 20.07.10 15:27:17, Cyrill Gorcunov wrote:
> On Tue, Jul 20, 2010 at 08:50:47PM +0200, Robert Richter wrote:
> >
> > This patch series contains some cleanups and reworks I made during
> > code review and feature implementation for upcoming cpus.
> > 
> > Most patches refactor the xsave initialization that is very dependent
> > on fpu initialization. This series starts to decouple this a little
> > bit as xsave not only supports fpu features. Also this is an attempt
> > to ease the xsave interface by making some of the functions and
> > variables static.
> > 
> > There is also one patch that removes boot_cpu_id variable, which is
> > not really related to xsave. Maybe this should be applied to another
> > branch.
> > 
> > The patches are relative to today's tip/x86/xsave branch.
> > 
> > (The patches are small for better review and rebasing.)
> > 
> > -Robert
> > 
> 
> Hi Robert, I recall there was a thread related to boot_cpu_id and
> cpu = 0. Unfortunately I can't find it neither in my mbox nor somewhere
> in net at moment.

I found this patch:

 b3572e3 x86/voyager: fix compile breakage caused by dc1e35c6e95e8923cf1d3510438b63c600fee1e2

indicating that boot cpu id could be different than 0.

But either this is broken again, or the issue is gone in a different
way.

> Ie technically speaking -- yes boot_cpu_id will be 0
> but perhaps instead of magic !cpu and friends explicit boot_cpu_id might
> be better for code reading. It might be is_boot_cpu() macro helper or
> so as well.
> 
> Though I don't have strong opinion but for ones who will be
> reading the code first time it might be confusing :) Agreed?

That's true, but once you know...

I could make a follow on patch with an is_boot_cpu() macro. Ingo, what
do you think?

But first question is, is it always !smp_processor_id()? At least
current implementation indicates this:

 void __cpuinit identify_secondary_cpu(struct cpuinfo_x86 *c)
 {
 	BUG_ON(c == &boot_cpu_data);
 	...

with:

 #define boot_cpu_data cpu_data[0]

... which is valid for 32 and 64 bit.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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