Re: CPU hotplug on i386

[Nathan Lynch <ntl@pobox.com>]

Hi again-

On Wed, Mar 16, 2005 at 02:21:52PM +0100, Pavel Machek wrote:
> +	int cpu, error;
> +	cpus_clear(frozen_cpus);
> +	printk("Freezing cpus...\n");
> +	for_each_online_cpu(cpu) {
> +		if (!cpu)
> +			continue;
> +		cpu_set(cpu, frozen_cpus);
> +		error = cpu_down(cpu);
> +		if (!error)
> +			continue;
> +		printk("Error taking cpu %d down: %d\n", cpu, error);
> +		panic("Too many cpus");
>  	}
> -	printk("ok\n");
> +	BUG_ON(smp_processor_id() != 0);
>  }
>  
>  void enable_nonboot_cpus(void)
>  {
> -	printk("Restarting CPUs");
> -	atomic_set(&freeze, 0);
> -	while (atomic_read(&cpu_counter)) {
> -		cpu_relax();
> -		barrier();
> +	int cpu, error;
> +	printk("Thawing cpus...\n");
> +	for_each_cpu_mask(cpu, frozen_cpus) {
> +		if (!cpu)
> +			continue;
> +		error = cpu_up(cpu);
> +		if (!error)
> +			continue;
> +		printk("Error taking cpu %d up: %d\n", cpu, error);
> +		panic("Not enough cpus");
>  	}

If you're going to depend on CONFIG_HOTPLUG_CPU for swsusp on smp, why
not offline the non-boot cpus from userspace?  Same goes for onlining
additional cpus during resume.

Nathan