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authorGautham R Shenoy <ego@in.ibm.com>2008-01-25 15:08:02 -0500
committerIngo Molnar <mingo@elte.hu>2008-01-25 15:08:02 -0500
commit86ef5c9a8edd78e6bf92879f32329d89b2d55b5a (patch)
tree7bf46885326a6fdbb0c3596855408e9a5634dd3a /Documentation/cpu-hotplug.txt
parentd221938c049f4845da13c8593132595a6b9222a8 (diff)
cpu-hotplug: replace lock_cpu_hotplug() with get_online_cpus()
Replace all lock_cpu_hotplug/unlock_cpu_hotplug from the kernel and use get_online_cpus and put_online_cpus instead as it highlights the refcount semantics in these operations. The new API guarantees protection against the cpu-hotplug operation, but it doesn't guarantee serialized access to any of the local data structures. Hence the changes needs to be reviewed. In case of pseries_add_processor/pseries_remove_processor, use cpu_maps_update_begin()/cpu_maps_update_done() as we're modifying the cpu_present_map there. Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'Documentation/cpu-hotplug.txt')
-rw-r--r--Documentation/cpu-hotplug.txt11
1 files changed, 6 insertions, 5 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index a741f658a3c9..fb94f5a71b68 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -109,12 +109,13 @@ Never use anything other than cpumask_t to represent bitmap of CPUs.
109 for_each_cpu_mask(x,mask) - Iterate over some random collection of cpu mask. 109 for_each_cpu_mask(x,mask) - Iterate over some random collection of cpu mask.
110 110
111 #include <linux/cpu.h> 111 #include <linux/cpu.h>
112 lock_cpu_hotplug() and unlock_cpu_hotplug(): 112 get_online_cpus() and put_online_cpus():
113 113
114The above calls are used to inhibit cpu hotplug operations. While holding the 114The above calls are used to inhibit cpu hotplug operations. While the
115cpucontrol mutex, cpu_online_map will not change. If you merely need to avoid 115cpu_hotplug.refcount is non zero, the cpu_online_map will not change.
116cpus going away, you could also use preempt_disable() and preempt_enable() 116If you merely need to avoid cpus going away, you could also use
117for those sections. Just remember the critical section cannot call any 117preempt_disable() and preempt_enable() for those sections.
118Just remember the critical section cannot call any
118function that can sleep or schedule this process away. The preempt_disable() 119function that can sleep or schedule this process away. The preempt_disable()
119will work as long as stop_machine_run() is used to take a cpu down. 120will work as long as stop_machine_run() is used to take a cpu down.
120 121