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

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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: Mike Travis <travis@sgi.com>
This commit is contained in:
Mike Travis 2008-12-17 15:21:39 -08:00 committed by Ingo Molnar
parent a775a38b13
commit 3b11ce7f54
3 changed files with 42 additions and 20 deletions
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17
Documentation/cpu-hotplug.txt
View file

@ -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.

20
arch/x86/kernel/apic.c
View file

@ -1819,28 +1819,32 @@ 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
*/
if (version == 0x0) {
pr_warning("BIOS bug, APIC version is 0 for CPU#%d! "
"fixing up to 0x10. (tell your hw vendor)\n",
version);
"fixing up to 0x10. (tell your hw vendor)\n",
version);
version = 0x10;
}
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) {

25
arch/x86/kernel/smpboot.c
View file

@ -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;
possible = num_processors + disabled_cpus;
if (possible > NR_CPUS)
possible = NR_CPUS;
if (setup_possible_cpus == -1)
possible = num_processors + disabled_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));