diff options
authorPaul Jackson <pj@sgi.com>2006-08-27 01:23:51 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-08-27 11:01:32 -0700
commit4c4d50f7b39cc58f1064b93a61ad617451ae41df (patch)
parent6394cca54894f6a9bcf927ab78d28985944298ff (diff)
[PATCH] cpuset: top_cpuset tracks hotplug changes to cpu_online_map
Change the list of cpus allowed to tasks in the top (root) cpuset to dynamically track what cpus are online, using a CPU hotplug notifier. Make this top cpus file read-only. On systems that have cpusets configured in their kernel, but that aren't actively using cpusets (for some distros, this covers the majority of systems) all tasks end up in the top cpuset. If that system does support CPU hotplug, then these tasks cannot make use of CPUs that are added after system boot, because the CPUs are not allowed in the top cpuset. This is a surprising regression over earlier kernels that didn't have cpusets enabled. In order to keep the behaviour of cpusets consistent between systems actively making use of them and systems not using them, this patch changes the behaviour of the 'cpus' file in the top (root) cpuset, making it read only, and making it automatically track the value of cpu_online_map. Thus tasks in the top cpuset will have automatic use of hot plugged CPUs allowed by their cpuset. Thanks to Anton Blanchard and Nathan Lynch for reporting this problem, driving the fix, and earlier versions of this patch. Signed-off-by: Paul Jackson <pj@sgi.com> Cc: Nathan Lynch <ntl@pobox.com> Cc: Anton Blanchard <anton@samba.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2 files changed, 39 insertions, 0 deletions
diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index 159e2a0c3e80..76b44290c154 100644
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -217,6 +217,12 @@ exclusive cpuset. Also, the use of a Linux virtual file system (vfs)
to represent the cpuset hierarchy provides for a familiar permission
and name space for cpusets, with a minimum of additional kernel code.
+The cpus file in the root (top_cpuset) cpuset is read-only.
+It automatically tracks the value of cpu_online_map, using a CPU
+hotplug notifier. If and when memory nodes can be hotplugged,
+we expect to make the mems file in the root cpuset read-only
+as well, and have it track the value of node_online_map.
1.4 What are exclusive cpusets ?
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 1a649f2bb9bb..f1dda98bdffe 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -816,6 +816,10 @@ static int update_cpumask(struct cpuset *cs, char *buf)
struct cpuset trialcs;
int retval, cpus_unchanged;
+ /* top_cpuset.cpus_allowed tracks cpu_online_map; it's read-only */
+ if (cs == &top_cpuset)
+ return -EACCES;
trialcs = *cs;
retval = cpulist_parse(buf, trialcs.cpus_allowed);
if (retval < 0)
@@ -2033,6 +2037,33 @@ out:
return err;
+ * The top_cpuset tracks what CPUs and Memory Nodes are online,
+ * period. This is necessary in order to make cpusets transparent
+ * (of no affect) on systems that are actively using CPU hotplug
+ * but making no active use of cpusets.
+ *
+ * This handles CPU hotplug (cpuhp) events. If someday Memory
+ * Nodes can be hotplugged (dynamically changing node_online_map)
+ * then we should handle that too, perhaps in a similar way.
+ */
+static int cpuset_handle_cpuhp(struct notifier_block *nb,
+ unsigned long phase, void *cpu)
+ mutex_lock(&manage_mutex);
+ mutex_lock(&callback_mutex);
+ top_cpuset.cpus_allowed = cpu_online_map;
+ mutex_unlock(&callback_mutex);
+ mutex_unlock(&manage_mutex);
+ return 0;
* cpuset_init_smp - initialize cpus_allowed
@@ -2043,6 +2074,8 @@ void __init cpuset_init_smp(void)
top_cpuset.cpus_allowed = cpu_online_map;
top_cpuset.mems_allowed = node_online_map;
+ hotcpu_notifier(cpuset_handle_cpuhp, 0);