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

Ashok Raj
2004-11-05T02:02:09Z

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@austin.ibm.com>
>
>
> ---
>
>
> +
> +/*
> + * 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