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

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Date:	Wed, 21 Jul 2010 20:29:56 +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 Wed, Jul 21, 2010 at 06:16:54PM +0200, Robert Richter wrote:
> On 20.07.10 16:17:40, Cyrill Gorcunov wrote:
> 
> > note the snippet
> > 
> > 		if (cpu == boot_cpu_id)
> > 			switch_to_new_gdt(cpu);
> > 
> > but cycle of assignment is done over all possible cpus so
> > smp_processor_id will be = 0 for BP but definitely it's
> > confusing and better to check for BP via explicit cpu == boot_cpu_id
> > I think. Though I might be missing something.
> 
> This in smpboot.c makes it clear:
> 
> void __cpuinit smp_store_cpu_info(int id)
> {
>         struct cpuinfo_x86 *c = &cpu_data(id);
> 
>         copy_cpuinfo_x86(c, &boot_cpu_data);
>         c->cpu_index = id;
>         if (id != 0)
>                 identify_secondary_cpu(c);
> }
> 
> So boot cpu id is always 0.

yeah, thanks!

> 
> Also note, as Hans Peter already pointed out, this for CONFIG_SMP:
> 
>  &cpu_data(0) != &boot_cpu_data
> 
> The data in boot_cpu_data is (partly) already available after
> early_cpu_init(). It is later copied to the &cpu_data() structures. So
> boot_cpu_data should be used for init code.
> 
> Also, to make the test obviously, instead of testing (cpu ==
> boot_cpu_id) I rather tend to use an is_boot_cpu() macro as you
> suggested in your earlier mail.
> 
> -Robert
> 
> -- 
> Advanced Micro Devices, Inc.
> Operating System Research Center
> 

ok, thanks Robert!

	-- Cyrill
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