linux-kernel - Re: [PATCH v7 04/12] Don't offline CPU0 if any PIC irq can not be migrated out of it.

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Date:	Fri, 24 Aug 2012 11:39:28 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Fenghua Yu <fenghua.yu@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Asit K Mallick <asit.k.mallick@...el.com>,
	Tony Luck <tony.luck@...el.com>,
	Arjan Dan De Ven <arjan@...ux.intel.com>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Len Brown <len.brown@...el.com>,
	"Srivatssa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Chen Gong <gong.chen@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v7 04/12] Don't offline CPU0 if any PIC irq can not be
 migrated out of it.

On Thu, Aug 23, 2012 at 05:56:03PM -0700, Fenghua Yu wrote:
> From: Fenghua Yu <fenghua.yu@...el.com>
> 
> Change smp_store_cpu_info() to store cpu info for a CPU when it's brought up.
> This includes bringing up CPU0 or AP after it's offline. But don't store cpu
> info when BSP first boots during boot time.
> 
> Continue to online CPU0 in native_cpu_up().
> 
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> ---
>  arch/x86/include/asm/smp.h |    2 +-
>  arch/x86/kernel/smpboot.c  |   32 +++++++++++---------------------
>  2 files changed, 12 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index 4f19a15..0be0b29 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -166,7 +166,7 @@ void native_send_call_func_ipi(const struct cpumask *mask);
>  void native_send_call_func_single_ipi(int cpu);
>  void x86_idle_thread_init(unsigned int cpu, struct task_struct *idle);
>  
> -void smp_store_cpu_info(int id);
> +void smp_store_cpu_info(int id, int store);
>  #define cpu_physical_id(cpu)	per_cpu(x86_cpu_to_apicid, cpu)
>  
>  #else /* !CONFIG_SMP */
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index c80a33b..8d0b4ff 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -125,8 +125,8 @@ EXPORT_PER_CPU_SYMBOL(cpu_info);
>  atomic_t init_deasserted;
>  
>  /*
> - * Report back to the Boot Processor.
> - * Running on AP.
> + * Report back to the Boot Processor during boot time or to the caller processor
> + * during CPU online.
>   */
>  static void __cpuinit smp_callin(void)
>  {
> @@ -201,7 +201,7 @@ static void __cpuinit smp_callin(void)
>  	 * Save our processor parameters. Note: this information
>  	 * is needed for clock calibration.
>  	 */
> -	smp_store_cpu_info(cpuid);
> +	smp_store_cpu_info(cpuid, 1);
>  
>  	/*
>  	 * Get our bogomips.
> @@ -283,14 +283,17 @@ notrace static void __cpuinit start_secondary(void *unused)
>   * The bootstrap kernel entry code has set these up. Save them for
>   * a given CPU
>   */
> -
> -void __cpuinit smp_store_cpu_info(int id)
> +void __cpuinit smp_store_cpu_info(int id, int store)

This usage begs for "bool store".

>  {
>  	struct cpuinfo_x86 *c = &cpu_data(id);
>  
>  	*c = boot_cpu_data;
>  	c usage->cpu_index = id;
> -	if (id != 0)
> +	/*
> +	 * During boot time, CPU0 has this setup already. Save the info when
> +	 * bringing up AP or offlined CPU0.
> +	 */
> +	if (store)
>  		identify_secondary_cpu(c);
>  }
>  
> @@ -795,7 +798,7 @@ int __cpuinit native_cpu_up(unsigned int cpu, struct task_struct *tidle)
>  
>  	pr_debug("++++++++++++++++++++=_---CPU UP  %u\n", cpu);
>  
> -	if (apicid == BAD_APICID || apicid == boot_cpu_physical_apicid ||
> +	if (apicid == BAD_APICID ||
>  	    !physid_isset(apicid, phys_cpu_present_map) ||
>  	    !apic->apic_id_valid(apicid)) {

Nothing in the commit message explains this change...

>  		pr_err("%s: bad cpu %d\n", __func__, cpu);
> @@ -990,7 +993,7 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
>  	/*
>  	 * Setup boot CPU information
>  	 */
> -	smp_store_cpu_info(0); /* Final full version of the data */
> +	smp_store_cpu_info(0, 0); /* Final full version of the data */
>  	cpumask_copy(cpu_callin_mask, cpumask_of(0));
>  	mb();
>  
> @@ -1214,19 +1217,6 @@ void cpu_disable_common(void)
>  
>  int native_cpu_disable(void)
>  {
> -	int cpu = smp_processor_id();
> -
> -	/*
> -	 * Perhaps use cpufreq to drop frequency, but that could go
> -	 * into generic code.
> -	 *
> -	 * We won't take down the boot processor on i386 due to some
> -	 * interrupts only being able to be serviced by the BSP.
> -	 * Especially so if we're not using an IOAPIC	-zwane
> -	 */
> -	if (cpu == 0)
> -		return -EBUSY;
> -
>  	clear_local_APIC();
>  
>  	cpu_disable_common();
> -- 
> 1.7.2
> 
> --
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-- 
Regards/Gruss,
    Boris.
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