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Message-ID: <20121203161845.GE17093@dhcp22.suse.cz>
Date: Mon, 3 Dec 2012 17:18:45 +0100
From: Michal Hocko <mhocko@...e.cz>
To: Tejun Heo <tj@...nel.org>
Cc: lizefan@...wei.com, paul@...lmenage.org, glommer@...allels.com,
containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] cpuset: replace cpuset->stack_list with
cpuset_for_each_descendant_pre()
On Wed 28-11-12 14:27:00, Tejun Heo wrote:
> Implement cpuset_for_each_descendant_pre() and replace the
> cpuset-specific tree walking using cpuset->stack_list with it.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
Reviewed-by: Michal Hocko <mhocko@...e.cz>
> ---
> kernel/cpuset.c | 123 ++++++++++++++++++++++----------------------------------
> 1 file changed, 48 insertions(+), 75 deletions(-)
>
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 2ee0e03..3a01730 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -103,9 +103,6 @@ struct cpuset {
> /* for custom sched domain */
> int relax_domain_level;
>
> - /* used for walking a cpuset hierarchy */
> - struct list_head stack_list;
> -
> struct work_struct hotplug_work;
> };
>
> @@ -207,6 +204,20 @@ static struct cpuset top_cpuset = {
> cgroup_for_each_child((pos_cgrp), (parent_cs)->css.cgroup) \
> if (is_cpuset_online(((child_cs) = cgroup_cs((pos_cgrp)))))
>
> +/**
> + * cpuset_for_each_descendant_pre - pre-order walk of a cpuset's descendants
> + * @des_cs: loop cursor pointing to the current descendant
> + * @pos_cgrp: used for iteration
> + * @root_cs: target cpuset to walk ancestor of
> + *
> + * Walk @des_cs through the online descendants of @root_cs. Must be used
> + * with RCU read locked. The caller may modify @pos_cgrp by calling
> + * cgroup_rightmost_descendant() to skip subtree.
> + */
> +#define cpuset_for_each_descendant_pre(des_cs, pos_cgrp, root_cs) \
> + cgroup_for_each_descendant_pre((pos_cgrp), (root_cs)->css.cgroup) \
> + if (is_cpuset_online(((des_cs) = cgroup_cs((pos_cgrp)))))
> +
> /*
> * There are two global mutexes guarding cpuset structures - cpuset_mutex
> * and callback_mutex. The latter may nest inside the former. We also
> @@ -507,31 +518,24 @@ update_domain_attr(struct sched_domain_attr *dattr, struct cpuset *c)
> return;
> }
>
> -static void
> -update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
> +static void update_domain_attr_tree(struct sched_domain_attr *dattr,
> + struct cpuset *root_cs)
> {
> - LIST_HEAD(q);
> -
> - list_add(&c->stack_list, &q);
> - while (!list_empty(&q)) {
> - struct cpuset *cp;
> - struct cgroup *cont;
> - struct cpuset *child;
> -
> - cp = list_first_entry(&q, struct cpuset, stack_list);
> - list_del(q.next);
> + struct cpuset *cp;
> + struct cgroup *pos_cgrp;
>
> - if (cpumask_empty(cp->cpus_allowed))
> + rcu_read_lock();
> + cpuset_for_each_descendant_pre(cp, pos_cgrp, root_cs) {
> + /* skip the whole subtree if @cp doesn't have any CPU */
> + if (cpumask_empty(cp->cpus_allowed)) {
> + pos_cgrp = cgroup_rightmost_descendant(pos_cgrp);
> continue;
> + }
>
> if (is_sched_load_balance(cp))
> update_domain_attr(dattr, cp);
> -
> - rcu_read_lock();
> - cpuset_for_each_child(child, cont, cp)
> - list_add_tail(&child->stack_list, &q);
> - rcu_read_unlock();
> }
> + rcu_read_unlock();
> }
>
> /*
> @@ -591,7 +595,6 @@ update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
> static int generate_sched_domains(cpumask_var_t **domains,
> struct sched_domain_attr **attributes)
> {
> - LIST_HEAD(q); /* queue of cpusets to be scanned */
> struct cpuset *cp; /* scans q */
> struct cpuset **csa; /* array of all cpuset ptrs */
> int csn; /* how many cpuset ptrs in csa so far */
> @@ -600,6 +603,7 @@ static int generate_sched_domains(cpumask_var_t **domains,
> struct sched_domain_attr *dattr; /* attributes for custom domains */
> int ndoms = 0; /* number of sched domains in result */
> int nslot; /* next empty doms[] struct cpumask slot */
> + struct cgroup *pos_cgrp;
>
> doms = NULL;
> dattr = NULL;
> @@ -627,33 +631,27 @@ static int generate_sched_domains(cpumask_var_t **domains,
> goto done;
> csn = 0;
>
> - list_add(&top_cpuset.stack_list, &q);
> - while (!list_empty(&q)) {
> - struct cgroup *cont;
> - struct cpuset *child; /* scans child cpusets of cp */
> -
> - cp = list_first_entry(&q, struct cpuset, stack_list);
> - list_del(q.next);
> -
> - if (cpumask_empty(cp->cpus_allowed))
> - continue;
> -
> + rcu_read_lock();
> + cpuset_for_each_descendant_pre(cp, pos_cgrp, &top_cpuset) {
> /*
> - * All child cpusets contain a subset of the parent's cpus, so
> - * just skip them, and then we call update_domain_attr_tree()
> - * to calc relax_domain_level of the corresponding sched
> - * domain.
> + * Continue traversing beyond @cp iff @cp has some CPUs and
> + * isn't load balancing. The former is obvious. The
> + * latter: All child cpusets contain a subset of the
> + * parent's cpus, so just skip them, and then we call
> + * update_domain_attr_tree() to calc relax_domain_level of
> + * the corresponding sched domain.
> */
> - if (is_sched_load_balance(cp)) {
> - csa[csn++] = cp;
> + if (!cpumask_empty(cp->cpus_allowed) &&
> + !is_sched_load_balance(cp))
> continue;
> - }
>
> - rcu_read_lock();
> - cpuset_for_each_child(child, cont, cp)
> - list_add_tail(&child->stack_list, &q);
> - rcu_read_unlock();
> - }
> + if (is_sched_load_balance(cp))
> + csa[csn++] = cp;
> +
> + /* skip @cp's subtree */
> + pos_cgrp = cgroup_rightmost_descendant(pos_cgrp);
> + }
> + rcu_read_unlock();
>
> for (i = 0; i < csn; i++)
> csa[i]->pn = i;
> @@ -2059,31 +2057,6 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
> move_member_tasks_to_cpuset(cs, parent);
> }
>
> -/*
> - * Helper function to traverse cpusets.
> - * It can be used to walk the cpuset tree from top to bottom, completing
> - * one layer before dropping down to the next (thus always processing a
> - * node before any of its children).
> - */
> -static struct cpuset *cpuset_next(struct list_head *queue)
> -{
> - struct cpuset *cp;
> - struct cpuset *child; /* scans child cpusets of cp */
> - struct cgroup *cont;
> -
> - if (list_empty(queue))
> - return NULL;
> -
> - cp = list_first_entry(queue, struct cpuset, stack_list);
> - list_del(queue->next);
> - rcu_read_lock();
> - cpuset_for_each_child(child, cont, cp)
> - list_add_tail(&child->stack_list, queue);
> - rcu_read_unlock();
> -
> - return cp;
> -}
> -
> /**
> * cpuset_propagate_hotplug_workfn - propagate CPU/memory hotplug to a cpuset
> * @cs: cpuset in interest
> @@ -2220,12 +2193,12 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
> /* if cpus or mems went down, we need to propagate to descendants */
> if (cpus_offlined || mems_offlined) {
> struct cpuset *cs;
> - LIST_HEAD(queue);
> + struct cgroup *pos_cgrp;
>
> - list_add_tail(&top_cpuset.stack_list, &queue);
> - while ((cs = cpuset_next(&queue)))
> - if (cs != &top_cpuset)
> - schedule_cpuset_propagate_hotplug(cs);
> + rcu_read_lock();
> + cpuset_for_each_descendant_pre(cs, pos_cgrp, &top_cpuset)
> + schedule_cpuset_propagate_hotplug(cs);
> + rcu_read_unlock();
> }
>
> mutex_unlock(&cpuset_mutex);
> --
> 1.7.11.7
>
> --
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--
Michal Hocko
SUSE Labs
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