Re: [PATCH 7/9] x86/topology.c: Support functions for BSP online/offline

From: Srivatsa S. Bhat
Date: Sat Nov 05 2011 - 07:01:43 EST


On 11/05/2011 03:33 AM, Fenghua Yu wrote:
> From: Fenghua Yu <fenghua.yu@xxxxxxxxx>
>
> By default, BSP can't be hotpluggable because bsp_hotpluggable is 0. Kernel
> parameter bsp_hotplug can enable BSP hotplug feature.
>
> arch_cpu_maps_update_begin() and arch_cpu_maps_update_done() locks/unlocks
> pm_mutex. This solves cpu maps race condition between BSP online check during
> hibernate/suspend and BSP online/offline operations.
>
> arch_state_check() checks if BSP is still the first online CPU.
>
> Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> ---
> arch/x86/kernel/topology.c | 44 +++++++++++++++++++++++++++++++++++++-------
> 1 files changed, 37 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
> index 8927486..287d7b6 100644
> --- a/arch/x86/kernel/topology.c
> +++ b/arch/x86/kernel/topology.c
> @@ -29,23 +29,53 @@
> #include <linux/mmzone.h>
> #include <linux/init.h>
> #include <linux/smp.h>
> +#include <linux/suspend.h>
> #include <asm/cpu.h>
>
> static DEFINE_PER_CPU(struct x86_cpu, cpu_devices);
>
> #ifdef CONFIG_HOTPLUG_CPU
> +
> +static int bsp_hotpluggable;
> +
> +static int __init enable_bsp_hotplug(char *str)
> +{
> + bsp_hotpluggable = 1;
> + return 0;
> +}
> +
> +__setup("bsp_hotplug", enable_bsp_hotplug);
> +
> +void arch_cpu_maps_update_begin(void)
> +{
> + lock_system_sleep();
> +}
> +
> +void arch_cpu_maps_update_done(void)
> +{
> + unlock_system_sleep();
> +}
> +
> +int arch_state_check(void)
> +{
> + if (cpumask_first(cpu_online_mask) != 0) {
> + printk(KERN_WARNING "No CPU0.\n");

How about a better warning, perhaps like "CPU0 is offline"
or something like that?

> + return -ENODEV;
> + }
> +
> + return 0;
> +}
> +
> int __ref arch_register_cpu(int num)
> {
> /*
> - * CPU0 cannot be offlined due to several
> - * restrictions and assumptions in kernel. This basically
> - * doesn't add a control file, one cannot attempt to offline
> - * BSP.
> + * Suspend/resume depends on BSP. PIC interrupts depend on BSP.
> *
> - * Also certain PCI quirks require not to enable hotplug control
> - * for all CPU's.
> + * If the BSP depencies are under control, tell kernel to
> + * enable BSP hotplug. This basically adds a control file and
> + * one can attempt to offline BSP.
> */
> - if (num)
> + if (num || bsp_hotpluggable)
> per_cpu(cpu_devices, num).cpu.hotpluggable = 1;
>
> return register_cpu(&per_cpu(cpu_devices, num).cpu, num);

Thanks,
Srivatsa S. Bhat

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