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

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Message-ID: <20100721161654.GR26154@erda.amd.com>
Date:	Wed, 21 Jul 2010 18:16:54 +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 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.

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

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