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Subject[PATCH 2/3] x86: use possible_cpus=NUM to extend the possible cpus allowed
Impact: allow adding additional cpus.

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.

Based on tip/cpus4096 + .../rusty/linux-2.6-for-ingo.git/master +
x86-only-patches sent 12/15.

Signed-off-by: Mike Travis <travis@sgi.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Rusty Russell <rusty@rustycorp.com.au>
---
Documentation/cpu-hotplug.txt | 17 +++++++++--------
arch/x86/kernel/apic.c | 16 ++++++++++------
arch/x86/kernel/smpboot.c | 25 +++++++++++++++++++++----
3 files changed, 40 insertions(+), 18 deletions(-)
--- linux-2.6-for-ingo.orig/Documentation/cpu-hotplug.txt
+++ linux-2.6-for-ingo/Documentation/cpu-hotplug.txt
@@ -50,16 +50,17 @@ additional_cpus=n (*) Use this to limit
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.
--- linux-2.6-for-ingo.orig/arch/x86/kernel/apic.c
+++ linux-2.6-for-ingo/arch/x86/kernel/apic.c
@@ -1832,7 +1832,6 @@ void disconnect_bsp_APIC(int virt_wire_s
void __cpuinit generic_processor_info(int apicid, int version)
{
int cpu;
- cpumask_t tmp_map;

/*
* Validate version
@@ -1845,15 +1844,20 @@ void __cpuinit generic_processor_info(in
}
apic_version[apicid] = version;

- if (num_processors >= NR_CPUS) {
- printk(KERN_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;
+
+ printk(KERN_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) {
--- linux-2.6-for-ingo.orig/arch/x86/kernel/smpboot.c
+++ linux-2.6-for-ingo/arch/x86/kernel/smpboot.c
@@ -1254,6 +1254,15 @@ void __init native_smp_cpus_done(unsigne
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
@@ -1266,7 +1275,7 @@ void __init native_smp_cpus_done(unsigne
*
* 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
@@ -1279,9 +1288,17 @@ __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));
--


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