Commit 5f054e31 authored by Rusty Russell's avatar Rusty Russell
Browse files

documentation: remove references to cpu_*_map. 



This has been obsolescent for a while, fix documentation and
misc comments.

Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 88d8cd52

Documentation/cgroups/cpusets.txt

+1 −1
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@@ -217,7 +217,7 @@ and name space for cpusets, with a minimum of additional kernel code. 


The cpus and mems files in the root (top_cpuset) cpuset are

read-only.  The cpus file automatically tracks the value of

cpu_online_map using a CPU hotplug notifier, and the mems file

cpu_online_mask using a CPU hotplug notifier, and the mems file

automatically tracks the value of node_states[N_HIGH_MEMORY]--i.e.,

nodes with memory--using the cpuset_track_online_nodes() hook.

Documentation/cpu-hotplug.txt

+11 −11
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@@ -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

arch/alpha/kernel/smp.c

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@@ -450,7 +450,7 @@ setup_smp(void) 
		smp_num_probed = 1;

	}



	printk(KERN_INFO "SMP: %d CPUs probed -- cpu_present_map = %lx\n",

	printk(KERN_INFO "SMP: %d CPUs probed -- cpu_present_mask = %lx\n",

	       smp_num_probed, cpumask_bits(cpu_present_mask)[0]);

}

arch/ia64/kernel/acpi.c

+1 −1
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@@ -839,7 +839,7 @@ static __init int setup_additional_cpus(char *s) 
early_param("additional_cpus", setup_additional_cpus);



/*

 * cpu_possible_map should be static, it cannot change as CPUs

 * cpu_possible_mask should be static, it cannot change as CPUs

 * are onlined, or offlined. The reason is per-cpu data-structures

 * are allocated by some modules at init time, and dont expect to

 * do this dynamically on cpu arrival/departure.

arch/mips/cavium-octeon/smp.c

+1 −1
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@@ -78,7 +78,7 @@ static inline void octeon_send_ipi_mask(const struct cpumask *mask, 
}



/**

 * Detect available CPUs, populate cpu_possible_map

 * Detect available CPUs, populate cpu_possible_mask

 */

static void octeon_smp_hotplug_setup(void)

{