smp: Use nr_cpus= to set nr_cpu_ids early
On x86, before prefill_possible_map(), nr_cpu_ids will be NR_CPUS aka
CONFIG_NR_CPUS.
Add nr_cpus= to set nr_cpu_ids. so we can simulate cpus <=8 are installed on
normal config.
-v2: accordging to Christoph, acpi_numa_init should use nr_cpu_ids in stead of
NR_CPUS.
-v3: add doc in kernel-parameters.txt according to Andrew.
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1265793639-15071-34-git-send-email-yinghai@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Tony Luck <tony.luck@intel.com>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 736d456..51bceb0 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1772,6 +1772,12 @@
purges which is reported from either PAL_VM_SUMMARY or
SAL PALO.
+ nr_cpus= [SMP] Maximum number of processors that an SMP kernel
+ could support. nr_cpus=n : n >= 1 limits the kernel to
+ supporting 'n' processors. Later in runtime you can not
+ use hotplug cpu feature to put more cpu back to online.
+ just like you compile the kernel NR_CPUS=n
+
nr_uarts= [SERIAL] maximum number of UARTs to be registered.
numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
diff --git a/arch/ia64/kernel/acpi.c b/arch/ia64/kernel/acpi.c
index 40574ae..605a08b 100644
--- a/arch/ia64/kernel/acpi.c
+++ b/arch/ia64/kernel/acpi.c
@@ -881,8 +881,8 @@
possible = available_cpus + additional_cpus;
- if (possible > NR_CPUS)
- possible = NR_CPUS;
+ if (possible > nr_cpu_ids)
+ possible = nr_cpu_ids;
printk(KERN_INFO "SMP: Allowing %d CPUs, %d hotplug CPUs\n",
possible, max((possible - available_cpus), 0));
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 678d0b8..eff2fe1 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1213,11 +1213,12 @@
total_cpus = max_t(int, possible, num_processors + disabled_cpus);
- if (possible > CONFIG_NR_CPUS) {
+ /* nr_cpu_ids could be reduced via nr_cpus= */
+ if (possible > nr_cpu_ids) {
printk(KERN_WARNING
"%d Processors exceeds NR_CPUS limit of %d\n",
- possible, CONFIG_NR_CPUS);
- possible = CONFIG_NR_CPUS;
+ possible, nr_cpu_ids);
+ possible = nr_cpu_ids;
}
printk(KERN_INFO "SMP: Allowing %d CPUs, %d hotplug CPUs\n",
diff --git a/drivers/acpi/numa.c b/drivers/acpi/numa.c
index 7ad48df..b872546 100644
--- a/drivers/acpi/numa.c
+++ b/drivers/acpi/numa.c
@@ -279,9 +279,9 @@
/* SRAT: Static Resource Affinity Table */
if (!acpi_table_parse(ACPI_SIG_SRAT, acpi_parse_srat)) {
acpi_table_parse_srat(ACPI_SRAT_TYPE_X2APIC_CPU_AFFINITY,
- acpi_parse_x2apic_affinity, NR_CPUS);
+ acpi_parse_x2apic_affinity, nr_cpu_ids);
acpi_table_parse_srat(ACPI_SRAT_TYPE_CPU_AFFINITY,
- acpi_parse_processor_affinity, NR_CPUS);
+ acpi_parse_processor_affinity, nr_cpu_ids);
ret = acpi_table_parse_srat(ACPI_SRAT_TYPE_MEMORY_AFFINITY,
acpi_parse_memory_affinity,
NR_NODE_MEMBLKS);
diff --git a/init/main.c b/init/main.c
index 8451878..05b5283 100644
--- a/init/main.c
+++ b/init/main.c
@@ -149,6 +149,20 @@
early_param("nosmp", nosmp);
+/* this is hard limit */
+static int __init nrcpus(char *str)
+{
+ int nr_cpus;
+
+ get_option(&str, &nr_cpus);
+ if (nr_cpus > 0 && nr_cpus < nr_cpu_ids)
+ nr_cpu_ids = nr_cpus;
+
+ return 0;
+}
+
+early_param("nr_cpus", nrcpus);
+
static int __init maxcpus(char *str)
{
get_option(&str, &setup_max_cpus);