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Subject[PATCH] nohz/cpuset: enable addition&removal of cpus while in adaptive nohz mode
Currently modifying cpuset.cpus mask of a cgroup does not
update the reference counters for adaptive nohz mode if the
cpuset already had cpuset.adaptive_nohz == 1. Fix it so that
cpus can be added or removed from a adaptive_nohz cpuset.

Apply to Frederic's nohz/cpuset-v2 kernel 3.3.0-rc7nohz/cpuset-v2+
(commit abd48ecb412ff023582e97442a02a7cb162a1c4e)

Signed-off-by: Hakan Akkan <hakanakkan@gmail.com>
---
kernel/cpuset.c | 107 ++++++++++++++++++++++++++++++++++++-------------------
1 files changed, 70 insertions(+), 37 deletions(-)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index aa8304d..1446210 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -862,6 +862,8 @@ static void update_tasks_cpumask(struct cpuset *cs, struct ptr_heap *heap)
cgroup_scan_tasks(&scan);
}

+static void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs);
+
/**
* update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
* @cs: the cpuset to consider
@@ -902,6 +904,11 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
return 0;

+ /*
+ * Update adaptive nohz bits.
+ */
+ update_nohz_cpus(cs,trialcs);
+
retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, NULL);
if (retval)
return retval;
@@ -1247,51 +1254,74 @@ static void cpu_exit_nohz(int cpu)
preempt_enable();
}

-static void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs)
+static void update_cpu_nohz_flag(int cpu, int adjust)
+{
+ int ref = (per_cpu(cpu_adaptive_nohz_ref, cpu) += adjust);
+ printk("cpu %d, adjust %d, ref %d\n", cpu, adjust, ref);
+
+ if (ref == 1 && adjust > 0) {
+ cpumask_set_cpu(cpu, &nohz_cpuset_mask);
+ /*
+ * The mask update needs to be visible right away
+ * so that this CPU is part of the cputime IPI
+ * update right now.
+ */
+ smp_mb();
+ } else if (!ref) {
+ /*
+ * The update to cpu_adaptive_nohz_ref must be
+ * visible right away. So that once we restart the tick
+ * from the IPI, it won't be stopped again due to cache
+ * update lag.
+ * FIXME: We probably need more to ensure this value is really
+ * visible right away.
+ */
+ smp_mb();
+ cpu_exit_nohz(cpu);
+ /*
+ * Now that the tick has been restarted and cputimes
+ * flushed, we don't need anymore to be part of the
+ * cputime flush IPI.
+ */
+ cpumask_clear_cpu(cpu, &nohz_cpuset_mask);
+ }
+}
+
+static void update_nohz_flag(struct cpuset *old_cs, struct cpuset *cs)
{
int cpu;
- int val;
+ int adjust;

if (is_adaptive_nohz(old_cs) == is_adaptive_nohz(cs))
return;

+ adjust = is_adaptive_nohz(cs) ? 1 : -1;
for_each_cpu(cpu, cs->cpus_allowed) {
- if (is_adaptive_nohz(cs))
- per_cpu(cpu_adaptive_nohz_ref, cpu) += 1;
- else
- per_cpu(cpu_adaptive_nohz_ref, cpu) -= 1;
-
- val = per_cpu(cpu_adaptive_nohz_ref, cpu);
-
- if (val == 1) {
- cpumask_set_cpu(cpu, &nohz_cpuset_mask);
- /*
- * The mask update needs to be visible right away
- * so that this CPU is part of the cputime IPI
- * update right now.
- */
- smp_mb();
- } else if (!val) {
- /*
- * The update to cpu_adaptive_nohz_ref must be
- * visible right away. So that once we restart the tick
- * from the IPI, it won't be stopped again due to cache
- * update lag.
- * FIXME: We probably need more to ensure this value is really
- * visible right away.
- */
- smp_mb();
- cpu_exit_nohz(cpu);
- /*
- * Now that the tick has been restarted and cputimes
- * flushed, we don't need anymore to be part of the
- * cputime flush IPI.
- */
- cpumask_clear_cpu(cpu, &nohz_cpuset_mask);
- }
+ update_cpu_nohz_flag(cpu, adjust);
}
}
+
+static void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs)
+{
+ int cpu;
+ cpumask_t cpus;
+
+ /*
+ * Only bother if the cpuset has adaptive nohz
+ */
+ if (!is_adaptive_nohz(cs))
+ return;
+
+ cpumask_xor(&cpus, old_cs->cpus_allowed, cs->cpus_allowed);
+
+ for_each_cpu(cpu, &cpus)
+ update_cpu_nohz_flag(cpu,
+ cpumask_test_cpu(cpu, cs->cpus_allowed) ? 1 : -1);
+}
#else
+static inline void update_nohz_flag(struct cpuset *old_cs, struct cpuset *cs)
+{
+}
static inline void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs)
{
}
@@ -1362,7 +1392,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
spread_flag_changed = ((is_spread_slab(cs) != is_spread_slab(trialcs))
|| (is_spread_page(cs) != is_spread_page(trialcs)));

- update_nohz_cpus(cs, trialcs);
+ update_nohz_flag(cs, trialcs);

mutex_lock(&callback_mutex);
cs->flags = trialcs->flags;
@@ -2006,7 +2036,8 @@ static struct cgroup_subsys_state *cpuset_create(
/*
* If the cpuset being removed has its flag 'sched_load_balance'
* enabled, then simulate turning sched_load_balance off, which
- * will call async_rebuild_sched_domains().
+ * will call async_rebuild_sched_domains(). Also update adaptive
+ * nohz flag.
*/

static void cpuset_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
@@ -2016,6 +2047,8 @@ static void cpuset_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
if (is_sched_load_balance(cs))
update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);

+ update_flag(CS_ADAPTIVE_NOHZ, cs, 0);
+
number_of_cpusets--;
free_cpumask_var(cs->cpus_allowed);
kfree(cs);


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