diff options
Diffstat (limited to 'Documentation/cpu-hotplug.txt')
| -rw-r--r-- | Documentation/cpu-hotplug.txt | 22 |
1 files changed, 11 insertions, 11 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt index a20bfd4..66ef8f3 100644 --- a/Documentation/cpu-hotplug.txt +++ b/Documentation/cpu-hotplug.txt @@ -47,7 +47,7 @@ maxcpus=n Restrict boot time cpus to n. Say if you have 4 cpus, using other cpus later online, read FAQ's for more info. additional_cpus=n (*) Use this to limit hotpluggable cpus. This option sets - cpu_possible_map = cpu_present_map + additional_cpus + cpu_possible_mask = cpu_present_mask + additional_cpus cede_offline={"off","on"} Use this option to disable/enable putting offlined processors to an extended H_CEDE state on @@ -64,11 +64,11 @@ 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. +cpu_possible_mask. 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 + cpu_possible_mask. Thus keeping the numbers of bits set constant even if the machine gets rebooted. CPU maps and such @@ -76,7 +76,7 @@ CPU maps and such [More on cpumaps and primitive to manipulate, please check include/linux/cpumask.h that has more descriptive text.] -cpu_possible_map: Bitmap of possible CPUs that can ever be available in the +cpu_possible_mask: Bitmap of possible CPUs that can ever be available in the system. This is used to allocate some boot time memory for per_cpu variables that aren't designed to grow/shrink as CPUs are made available or removed. Once set during boot time discovery phase, the map is static, i.e no bits @@ -84,13 +84,13 @@ are added or removed anytime. Trimming it accurately for your system needs upfront can save some boot time memory. See below for how we use heuristics in x86_64 case to keep this under check. -cpu_online_map: Bitmap of all CPUs currently online. Its set in __cpu_up() +cpu_online_mask: Bitmap of all CPUs currently online. Its set in __cpu_up() after a cpu is available for kernel scheduling and ready to receive interrupts from devices. Its cleared when a cpu is brought down using __cpu_disable(), before which all OS services including interrupts are migrated to another target CPU. -cpu_present_map: Bitmap of CPUs currently present in the system. Not all +cpu_present_mask: Bitmap of CPUs currently present in the system. Not all of them may be online. When physical hotplug is processed by the relevant subsystem (e.g ACPI) can change and new bit either be added or removed from the map depending on the event is hot-add/hot-remove. There are currently @@ -99,22 +99,22 @@ at which time hotplug is disabled. You really dont need to manipulate any of the system cpu maps. They should be read-only for most use. When setting up per-cpu resources almost always use -cpu_possible_map/for_each_possible_cpu() to iterate. +cpu_possible_mask/for_each_possible_cpu() to iterate. Never use anything other than cpumask_t to represent bitmap of CPUs. #include <linux/cpumask.h> - for_each_possible_cpu - Iterate over cpu_possible_map - for_each_online_cpu - Iterate over cpu_online_map - for_each_present_cpu - Iterate over cpu_present_map + for_each_possible_cpu - Iterate over cpu_possible_mask + for_each_online_cpu - Iterate over cpu_online_mask + for_each_present_cpu - Iterate over cpu_present_mask for_each_cpu_mask(x,mask) - Iterate over some random collection of cpu mask. #include <linux/cpu.h> get_online_cpus() and put_online_cpus(): The above calls are used to inhibit cpu hotplug operations. While the -cpu_hotplug.refcount is non zero, the cpu_online_map will not change. +cpu_hotplug.refcount is non zero, the cpu_online_mask will not change. If you merely need to avoid cpus going away, you could also use preempt_disable() and preempt_enable() for those sections. Just remember the critical section cannot call any |
