Re: [RFC/PATCH 3/4] introduce cpu_add and cpu_remove

[Ashok Raj]

On Sun, Oct 24, 2004 at 05:42:31AM -0400, Nathan Lynch wrote:
> 
> These functions safely update cpu_present_map (i.e. with the
> cpucontrol semaphore held) and register or unregister the cpu device
> as needed.  These are needed by systems which can add or remove cpus
> from the system after boot (e.g. ppc64 and ia64), and are intended to
> be called from the platform-specific code such as the ACPI or Open
> Firmware layers.
> 
> Signed-off-by: Nathan Lynch <nathanl@xxxxxxxxxxxxxx>
> 
> 
> ---
> 
> 
> +
> +/*
> + * Add a cpu to the system.  Return the number of the cpu added,
> + * or NR_CPUS if no more slots available.
> + */
> +unsigned int cpu_add(void)
> +{
> +	unsigned int cpu = NR_CPUS;
> +
> +	lock_cpu_hotplug();
> +
> +	if (num_present_cpus() == num_possible_cpus())
> +goto out;
> +
> +	for_each_cpu(cpu)
> +		if (!cpu_present(cpu))
> +			break;

     could we simplify this by

   cpus_compliment(cpu_compliment_map, cpu_present_map);
   cpu = first_cpu(cpu_compliment_map);

> +
> +	if (register_cpu(cpu)) {
> +		cpu = NR_CPUS;
> +		goto out;
> +	}
> +	cpu_set(cpu, cpu_present_map);

I would prefer that register_cpu is performed in arch side, as there may be other setup 
necessary to capture the hardware->logical associations before consuming these. 


> +out:
> +	unlock_cpu_hotplug();
> +	return cpu;
> +}
> +
> +/*
> + * Remove a cpu from the system.
> + */
> +void cpu_remove(unsigned int cpu)
> +{
> +	lock_cpu_hotplug();
> +
> +	BUG_ON(cpu_present(cpu));
> +
> +	unregister_cpu(cpu);
> +
> +	cpu_clear(cpu, cpu_present_map);
> +
> +	unlock_cpu_hotplug();
> +}
>  #else
>  static inline int cpu_run_sbin_hotplug(unsigned int cpu, const char *action)
>  {
> 
> _
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-- 
Cheers,
Ashok Raj
- Linux OS & Technology Team
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