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Diffstat (limited to 'Documentation/core-api/cpu_hotplug.rst')
| -rw-r--r-- | Documentation/core-api/cpu_hotplug.rst | 49 |
1 files changed, 26 insertions, 23 deletions
diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst index c6f4ba2fb32d..dcb0e379e5e8 100644 --- a/Documentation/core-api/cpu_hotplug.rst +++ b/Documentation/core-api/cpu_hotplug.rst @@ -40,12 +40,6 @@ Command Line Switches supplied here is lower than the number of physically available CPUs, then those CPUs can not be brought online later. -``additional_cpus=n`` - Use this to limit hotpluggable CPUs. This option sets - ``cpu_possible_mask = cpu_present_mask + additional_cpus`` - - This option is limited to the IA64 architecture. - ``possible_cpus=n`` This option sets ``possible_cpus`` bits in ``cpu_possible_mask``. @@ -127,17 +121,8 @@ bring CPU4 back online:: $ echo 1 > /sys/devices/system/cpu/cpu4/online smpboot: Booting Node 0 Processor 4 APIC 0x1 -The CPU is usable again. This should work on all CPUs. CPU0 is often special -and excluded from CPU hotplug. On X86 the kernel option -*CONFIG_BOOTPARAM_HOTPLUG_CPU0* has to be enabled in order to be able to -shutdown CPU0. Alternatively the kernel command option *cpu0_hotplug* can be -used. Some known dependencies of CPU0: - -* Resume from hibernate/suspend. Hibernate/suspend will fail if CPU0 is offline. -* PIC interrupts. CPU0 can't be removed if a PIC interrupt is detected. - -Please let Fenghua Yu <fenghua.yu@intel.com> know if you find any dependencies -on CPU0. +The CPU is usable again. This should work on all CPUs, but CPU0 is often special +and excluded from CPU hotplug. The CPU hotplug coordination ============================ @@ -404,8 +389,8 @@ multi-instance state the following function is available: * cpuhp_setup_state_multi(state, name, startup, teardown) The @state argument is either a statically allocated state or one of the -constants for dynamically allocated states - CPUHP_PREPARE_DYN, -CPUHP_ONLINE_DYN - depending on the state section (PREPARE, ONLINE) for +constants for dynamically allocated states - CPUHP_BP_PREPARE_DYN, +CPUHP_AP_ONLINE_DYN - depending on the state section (PREPARE, ONLINE) for which a dynamic state should be allocated. The @name argument is used for sysfs output and for instrumentation. The @@ -560,7 +545,7 @@ available: * cpuhp_state_remove_instance(state, node) * cpuhp_state_remove_instance_nocalls(state, node) -The arguments are the same as for the the cpuhp_state_add_instance*() +The arguments are the same as for the cpuhp_state_add_instance*() variants above. The functions differ in the way how the installed callbacks are treated: @@ -597,7 +582,7 @@ notifications on online and offline operations:: Setup and teardown a dynamically allocated state in the ONLINE section for notifications on offline operations:: - state = cpuhp_setup_state(CPUHP_ONLINE_DYN, "subsys:offline", NULL, subsys_cpu_offline); + state = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "subsys:offline", NULL, subsys_cpu_offline); if (state < 0) return state; .... @@ -606,7 +591,7 @@ for notifications on offline operations:: Setup and teardown a dynamically allocated state in the ONLINE section for notifications on online operations without invoking the callbacks:: - state = cpuhp_setup_state_nocalls(CPUHP_ONLINE_DYN, "subsys:online", subsys_cpu_online, NULL); + state = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "subsys:online", subsys_cpu_online, NULL); if (state < 0) return state; .... @@ -615,7 +600,7 @@ for notifications on online operations without invoking the callbacks:: Setup, use and teardown a dynamically allocated multi-instance state in the ONLINE section for notifications on online and offline operation:: - state = cpuhp_setup_state_multi(CPUHP_ONLINE_DYN, "subsys:online", subsys_cpu_online, subsys_cpu_offline); + state = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, "subsys:online", subsys_cpu_online, subsys_cpu_offline); if (state < 0) return state; .... @@ -750,6 +735,24 @@ will receive all events. A script like:: can process the event further. +When changes to the CPUs in the system occur, the sysfs file +/sys/devices/system/cpu/crash_hotplug contains '1' if the kernel +updates the kdump capture kernel list of CPUs itself (via elfcorehdr), +or '0' if userspace must update the kdump capture kernel list of CPUs. + +The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration +option. + +To skip userspace processing of CPU hot un/plug events for kdump +(i.e. the unload-then-reload to obtain a current list of CPUs), this sysfs +file can be used in a udev rule as follows: + + SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" + +For a CPU hot un/plug event, if the architecture supports kernel updates +of the elfcorehdr (which contains the list of CPUs), then the rule skips +the unload-then-reload of the kdump capture kernel. + Kernel Inline Documentations Reference ====================================== |