path: root/Documentation/cpu-hotplug.txt
diff options
authorGautham R Shenoy <ego@in.ibm.com>2009-10-29 19:22:53 +0000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2009-11-24 14:33:04 +1100
commit3aa565f53c396914a9406388efaa238e9c937fc6 (patch)
treec5860c47cb1c6545a07aad87004fd97af25959a4 /Documentation/cpu-hotplug.txt
parent69ddb57cbea0b3dd851ea5f1edd1e609ad4da04e (diff)
powerpc/pseries: Add hooks to put the CPU into an appropriate offline state
When a CPU is offlined on POWER currently, we call rtas_stop_self() and hand the CPU back to the resource pool. This path is used for DLPAR which will cause a change in the LPAR configuration which will be visible outside. This patch changes the default state a CPU is put into when it is offlined. On platforms which support ceding the processor to the hypervisor with latency hint specifier value, during a cpu offline operation, instead of calling rtas_stop_self(), we cede the vCPU to the hypervisor while passing a latency hint specifier value. The Hypervisor can use this hint to provide better energy savings. Also, during the offline operation, the control of the vCPU remains with the LPAR as oppposed to returning it to the resource pool. The patch achieves this by creating an infrastructure to set the preferred_offline_state() which can be either - CPU_STATE_OFFLINE: which is the current behaviour of calling rtas_stop_self() - CPU_STATE_INACTIVE: which cedes the vCPU to the hypervisor with the latency hint specifier. The codepath which wants to perform a DLPAR operation can set the preferred_offline_state() of a CPU to CPU_STATE_OFFLINE before invoking cpu_down(). The patch also provides a boot-time command line argument to disable/enable CPU_STATE_INACTIVE. Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> Signed-off-by: Nathan Fontenot <nfont@austin.ibm.com> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'Documentation/cpu-hotplug.txt')
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index 9d620c153b04..4d4a644b505e 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -49,6 +49,12 @@ maxcpus=n Restrict boot time cpus to n. Say if you have 4 cpus, using
additional_cpus=n (*) Use this to limit hotpluggable cpus. This option sets
cpu_possible_map = cpu_present_map + additional_cpus
+cede_offline={"off","on"} Use this option to disable/enable putting offlined
+ processors to an extended H_CEDE state on
+ supported pseries platforms.
+ If nothing is specified,
+ cede_offline is set to "on".
(*) Option valid only for following architectures
- ia64

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