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Commit 8f8b1138 authored by Ashok Raj's avatar Ashok Raj Committed by Tony Luck
Browse files

[IA64] Count disabled cpus as potential hot-pluggable CPUs 



Minor updates to earlier patch.
- Added to documentation to add ia64 as well.
- Minor clarification on how to use disabled cpus
- used plain max instead of max_t per Andew Morton.

Signed-off-by: default avatarAshok Raj <ashok.raj@intel.com>
Signed-off-by: default avatarTony Luck <tony.luck@intel.com>
parent 6f6d7582

Documentation/cpu-hotplug.txt

+12 −2
Original line number Diff line number Diff line
@@ -44,10 +44,20 @@ maxcpus=n Restrict boot time cpus to n. Say if you have 4 cpus, using 
             maxcpus=2 will only boot 2. You can choose to bring the

             other cpus later online, read FAQ's for more info.



additional_cpus=n	[x86_64 only] use this to limit hotpluggable cpus.

                        This option sets

additional_cpus*=n	Use this to limit hotpluggable cpus. This option sets

			cpu_possible_map = cpu_present_map + additional_cpus



(*) Option valid only for following architectures

- x86_64, ia64



ia64 and x86_64 use the number of disabled local apics in ACPI tables MADT

to determine the number of potentially hot-pluggable cpus. The implementation

should only rely on this to count the #of cpus, but *MUST* not rely on the

apicid values in those tables for disabled apics. In the event BIOS doesnt

mark such hot-pluggable cpus as disabled entries, one could use this

parameter "additional_cpus=x" to represent those cpus in the cpu_possible_map.





CPU maps and such

-----------------

[More on cpumaps and primitive to manipulate, please check

arch/ia64/kernel/acpi.c

+8 −11
Original line number Diff line number Diff line
@@ -794,24 +794,21 @@ __init void prefill_possible_map(void) 
	int possible, disabled_cpus;



	disabled_cpus = total_cpus - available_cpus;



 	if (additional_cpus == -1) {

 		if (disabled_cpus > 0) {

 			possible = total_cpus;

 		if (disabled_cpus > 0)

			additional_cpus = disabled_cpus;

		}

 		else {

			possible = available_cpus;

 		else

			additional_cpus = 0;

 	}

 	} else {



	possible = available_cpus + additional_cpus;

	}



	if (possible > NR_CPUS)

		possible = NR_CPUS;



	printk(KERN_INFO "SMP: Allowing %d CPUs, %d hotplug CPUs\n",

		possible,

	        max_t(int, additional_cpus, 0));

		possible, max((possible - available_cpus), 0));



	for (i = 0; i < possible; i++)

		cpu_set(i, cpu_possible_map);