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-rw-r--r--Documentation/cpu-hotplug.txt22
1 files changed, 19 insertions, 3 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index 08c5d04f3086..e71bc6cbbc5e 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -11,6 +11,8 @@
11 Joel Schopp <jschopp@austin.ibm.com> 11 Joel Schopp <jschopp@austin.ibm.com>
12 ia64/x86_64: 12 ia64/x86_64:
13 Ashok Raj <ashok.raj@intel.com> 13 Ashok Raj <ashok.raj@intel.com>
14 s390:
15 Heiko Carstens <heiko.carstens@de.ibm.com>
14 16
15Authors: Ashok Raj <ashok.raj@intel.com> 17Authors: Ashok Raj <ashok.raj@intel.com>
16Lots of feedback: Nathan Lynch <nathanl@austin.ibm.com>, 18Lots of feedback: Nathan Lynch <nathanl@austin.ibm.com>,
@@ -44,9 +46,23 @@ maxcpus=n Restrict boot time cpus to n. Say if you have 4 cpus, using
44 maxcpus=2 will only boot 2. You can choose to bring the 46 maxcpus=2 will only boot 2. You can choose to bring the
45 other cpus later online, read FAQ's for more info. 47 other cpus later online, read FAQ's for more info.
46 48
47additional_cpus=n [x86_64 only] use this to limit hotpluggable cpus. 49additional_cpus=n [x86_64, s390 only] use this to limit hotpluggable cpus.
48 This option sets 50 This option sets
49 cpu_possible_map = cpu_present_map + additional_cpus 51 cpu_possible_map = cpu_present_map + additional_cpus
52
53ia64 and x86_64 use the number of disabled local apics in ACPI tables MADT
54to determine the number of potentially hot-pluggable cpus. The implementation
55should only rely on this to count the #of cpus, but *MUST* not rely on the
56apicid values in those tables for disabled apics. In the event BIOS doesnt
57mark such hot-pluggable cpus as disabled entries, one could use this
58parameter "additional_cpus=x" to represent those cpus in the cpu_possible_map.
59
60
61possible_cpus=n [s390 only] use this to set hotpluggable cpus.
62 This option sets possible_cpus bits in
63 cpu_possible_map. Thus keeping the numbers of bits set
64 constant even if the machine gets rebooted.
65 This option overrides additional_cpus.
50 66
51CPU maps and such 67CPU maps and such
52----------------- 68-----------------