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

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Message-ID: <20100720200729.GD6227@lenovo>
Date:	Wed, 21 Jul 2010 00:07:29 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Robert Richter <robert.richter@....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 Tue, Jul 20, 2010 at 09:46:06PM +0200, Robert Richter wrote:
> 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.
> 

yeah, I forgot about voyager indeed but seems this is quite specific
to voyager trick

> 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...
> 

yes, but before 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:
> 

I guess so, since it's assigned from boot_cpu_id iirc

>  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.
> 

I suppose this is just self-protection for "what if something will go
wrong and this will be called on non-BP cpu".

> -Robert
> 
> -- 
> Advanced Micro Devices, Inc.
> Operating System Research Center
> 
	-- Cyrill
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