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Commit 3b11ce7f authored by Mike Travis's avatar Mike Travis Committed by Ingo Molnar
Browse files

x86: use possible_cpus=NUM to extend the possible cpus allowed 



Impact: add new boot parameter

Use possible_cpus=NUM kernel parameter to extend the number of possible
cpus.

The ability to HOTPLUG ON cpus that are "possible" but not "present" is
dealt with in a later patch.

Signed-off-by: default avatarMike Travis <travis@sgi.com>
parent a775a38b

Documentation/cpu-hotplug.txt

+9 −8
Original line number Diff line number Diff line
@@ -50,16 +50,17 @@ 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



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 doesn't

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.

ia64 uses 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 doesn't 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.



possible_cpus=n		[s390 only] use this to set hotpluggable cpus.

possible_cpus=n		[s390,x86_64] use this to set hotpluggable cpus.

			This option sets possible_cpus bits in

			cpu_possible_map. Thus keeping the numbers of bits set

			constant even if the machine gets rebooted.

arch/x86/kernel/apic.c

+12 −8
Original line number Diff line number Diff line
@@ -1819,7 +1819,6 @@ void disconnect_bsp_APIC(int virt_wire_setup) 
void __cpuinit generic_processor_info(int apicid, int version)

{

	int cpu;

	cpumask_t tmp_map;



	/*

	 * Validate version
@@ -1832,15 +1831,20 @@ void __cpuinit generic_processor_info(int apicid, int version) 
	}

	apic_version[apicid] = version;



	if (num_processors >= NR_CPUS) {

		pr_warning("WARNING: NR_CPUS limit of %i reached."

			"  Processor ignored.\n", NR_CPUS);

	if (num_processors >= nr_cpu_ids) {

		int max = nr_cpu_ids;

		int thiscpu = max + disabled_cpus;



		pr_warning(

			"ACPI: NR_CPUS/possible_cpus limit of %i reached."

			"  Processor %d/0x%x ignored.\n", max, thiscpu, apicid);



		disabled_cpus++;

		return;

	}



	num_processors++;

	cpus_complement(tmp_map, cpu_present_map);

	cpu = first_cpu(tmp_map);

	cpu = cpumask_next_zero(-1, cpu_present_mask);



	physid_set(apicid, phys_cpu_present_map);

	if (apicid == boot_cpu_physical_apicid) {

arch/x86/kernel/smpboot.c

+21 −4
Original line number Diff line number Diff line
@@ -1252,6 +1252,15 @@ void __init native_smp_cpus_done(unsigned int max_cpus) 
	check_nmi_watchdog();

}



static int __initdata setup_possible_cpus = -1;

static int __init _setup_possible_cpus(char *str)

{

	get_option(&str, &setup_possible_cpus);

	return 0;

}

early_param("possible_cpus", _setup_possible_cpus);





/*

 * cpu_possible_map should be static, it cannot change as cpu's

 * are onlined, or offlined. The reason is per-cpu data-structures
@@ -1264,7 +1273,7 @@ void __init native_smp_cpus_done(unsigned int max_cpus) 
 *

 * Three ways to find out the number of additional hotplug CPUs:

 * - If the BIOS specified disabled CPUs in ACPI/mptables use that.

 * - The user can overwrite it with additional_cpus=NUM

 * - The user can overwrite it with possible_cpus=NUM

 * - Otherwise don't reserve additional CPUs.

 * We do this because additional CPUs waste a lot of memory.

 * -AK
@@ -1277,9 +1286,17 @@ __init void prefill_possible_map(void) 
	if (!num_processors)

		num_processors = 1;



	if (setup_possible_cpus == -1)

		possible = num_processors + disabled_cpus;

	if (possible > NR_CPUS)

		possible = NR_CPUS;

	else

		possible = setup_possible_cpus;



	if (possible > CONFIG_NR_CPUS) {

		printk(KERN_WARNING

			"%d Processors exceeds NR_CPUS limit of %d\n",

			possible, CONFIG_NR_CPUS);

		possible = CONFIG_NR_CPUS;

	}



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

		possible, max_t(int, possible - num_processors, 0));