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    Subject[PATCH v2 1/7] cpusets, hotplug: Implement cpuset tree traversal in a helper function
    Date
    At present, the functions that deal with cpusets during CPU/Mem hotplug
    are quite messy, since a lot of the functionality is mixed up without clear
    separation. And this takes a toll on optimization as well. For example,
    the function cpuset_update_active_cpus() is called on both CPU offline and CPU
    online events; and it invokes scan_for_empty_cpusets(), which makes sense
    only for CPU offline events. And hence, the current code ends up unnecessarily
    traversing the cpuset tree during CPU online also.

    As a first step towards cleaning up those functions, encapsulate the cpuset
    tree traversal in a helper function, so as to facilitate upcoming changes.

    Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    Cc: stable@vger.kernel.org
    ---

    kernel/cpuset.c | 26 ++++++++++++++++++--------
    1 files changed, 18 insertions(+), 8 deletions(-)

    diff --git a/kernel/cpuset.c b/kernel/cpuset.c
    index 14f7070..23e5da6 100644
    --- a/kernel/cpuset.c
    +++ b/kernel/cpuset.c
    @@ -2000,6 +2000,23 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
    move_member_tasks_to_cpuset(cs, parent);
    }

    +static struct cpuset *traverse_cpusets(struct list_head *queue)
    +{
    + struct cpuset *cp;
    + struct cpuset *child; /* scans child cpusets of cp */
    + struct cgroup *cont;
    +
    + cp = list_first_entry(queue, struct cpuset, stack_list);
    + list_del(queue->next);
    + list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
    + child = cgroup_cs(cont);
    + list_add_tail(&child->stack_list, queue);
    + }
    +
    + return cp;
    +}
    +
    +
    /*
    * Walk the specified cpuset subtree and look for empty cpusets.
    * The tasks of such cpuset must be moved to a parent cpuset.
    @@ -2019,19 +2036,12 @@ static void scan_for_empty_cpusets(struct cpuset *root)
    {
    LIST_HEAD(queue);
    struct cpuset *cp; /* scans cpusets being updated */
    - struct cpuset *child; /* scans child cpusets of cp */
    - struct cgroup *cont;
    static nodemask_t oldmems; /* protected by cgroup_mutex */

    list_add_tail((struct list_head *)&root->stack_list, &queue);

    while (!list_empty(&queue)) {
    - cp = list_first_entry(&queue, struct cpuset, stack_list);
    - list_del(queue.next);
    - list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
    - child = cgroup_cs(cont);
    - list_add_tail(&child->stack_list, &queue);
    - }
    + cp = traverse_cpusets(&queue);

    /* Continue past cpusets with all cpus, mems online */
    if (cpumask_subset(cp->cpus_allowed, cpu_active_mask) &&


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