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Message-ID: <487EFDD0.2060101@cn.fujitsu.com>
Date: Thu, 17 Jul 2008 16:07:44 +0800
From: Li Zefan <lizf@...fujitsu.com>
To: Paul Jackson <pj@....com>,
Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
CC: LKML <linux-kernel@...r.kernel.org>,
Paul Menage <menage@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Lai Jiangshan <laijs@...fujitsu.com>
Subject: [RFC] [PATCH] cpuset: fix wrong calculation of relax domain level
When multiple cpusets are overlapping in their 'cpus' and hence they
form a single sched domain, the largest sched_relax_domain_level among
those should be used. But when top_cpuset's sched_load_balance is
set, its sched_relax_domain_level is used regardless other sub-cpusets'.
There are several proposals to solve this:
1) Travel the cpuset hierarchy to find the largest relax_domain_level
in rebuild_sched_domains(). But cpuset avoids hierarchy travelling
when top_cpuset.sched_load_balance is set.
2) Remember the largest relax_domain_level when we update a cpuset's
sched_load_balance, sched_relax_domain_level and cpus. This should
work, but seems a bit tricky and a bit ugly. (As this patch shows)
3) Don't treat this as a bug, but document this behavior.
Reported-by: Lai Jiangshan <laijs@...fujitsu.com>
Signed-off-by: Li Zefan <lizf@...fujitsu.com>
---
cpuset.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 48 insertions(+), 2 deletions(-)
--- linux-mm.orig/kernel/cpuset.c 2008-07-17 15:02:12.000000000 +0800
+++ linux-mm/kernel/cpuset.c 2008-07-17 15:01:18.000000000 +0800
@@ -69,6 +69,14 @@ int number_of_cpusets __read_mostly;
struct cgroup_subsys cpuset_subsys;
struct cpuset;
+/*
+ * Tracks # of cpusets in each relax domain level. This is to avoid
+ * travelling the cpuset hierachy in rebuild_sched_domains()
+ * when top_cpuset.sched_load_balance == 1.
+ */
+static unsigned int __cpusets_rd_lv[SD_LV_MAX+1];
+static unsigned int *cpusets_rd_lv = __cpusets_rd_lv + 1;
+
/* See "Frequency meter" comments, below. */
struct fmeter {
@@ -594,6 +602,14 @@ static void rebuild_sched_domains(void)
update_domain_attr(dattr, &top_cpuset);
}
*doms = top_cpuset.cpus_allowed;
+
+ for (i = SD_LV_MAX - 1; i >= 0; i--) {
+ if (cpusets_rd_lv[i] && dattr) {
+ dattr->relax_domain_level = i;
+ break;
+ }
+ }
+
goto rebuild;
}
@@ -807,6 +823,7 @@ static int update_cpumask(struct cpuset
struct cpuset trialcs;
int retval;
int is_load_balanced;
+ int cpus_empty_changed;
/* top_cpuset.cpus_allowed tracks cpu_online_map; it's read-only */
if (cs == &top_cpuset)
@@ -839,11 +856,20 @@ static int update_cpumask(struct cpuset
return 0;
is_load_balanced = is_sched_load_balance(&trialcs);
+ cpus_empty_changed = (cpus_empty(cs->cpus_allowed) !=
+ cpus_empty(trialcs.cpus_allowed));
mutex_lock(&callback_mutex);
cs->cpus_allowed = trialcs.cpus_allowed;
mutex_unlock(&callback_mutex);
+ if (is_load_balanced && cpus_empty_changed) {
+ if (cpus_empty(cs->cpus_allowed))
+ cpusets_rd_lv[cs->relax_domain_level]--;
+ else
+ cpusets_rd_lv[cs->relax_domain_level]++;
+ }
+
/*
* Scan tasks in the cpuset, and update the cpumasks of any
* that need an update.
@@ -1074,12 +1100,19 @@ int current_cpuset_is_being_rebound(void
static int update_relax_domain_level(struct cpuset *cs, s64 val)
{
+ int need_rebuild = (!cpus_empty(cs->cpus_allowed) &&
+ is_sched_load_balance(cs));
+
if (val < -1 || val >= SD_LV_MAX)
return -EINVAL;
if (val != cs->relax_domain_level) {
+ if (need_rebuild) {
+ cpusets_rd_lv[cs->relax_domain_level]--;
+ cpusets_rd_lv[val]++;
+ }
cs->relax_domain_level = val;
- if (!cpus_empty(cs->cpus_allowed) && is_sched_load_balance(cs))
+ if (need_rebuild)
rebuild_sched_domains();
}
@@ -1120,8 +1153,13 @@ static int update_flag(cpuset_flagbits_t
cs->flags = trialcs.flags;
mutex_unlock(&callback_mutex);
- if (cpus_nonempty && balance_flag_changed)
+ if (cpus_nonempty && balance_flag_changed) {
+ if (is_sched_load_balance(cs))
+ cpusets_rd_lv[cs->relax_domain_level]++;
+ else
+ cpusets_rd_lv[cs->relax_domain_level]--;
rebuild_sched_domains();
+ }
return 0;
}
@@ -1856,6 +1894,7 @@ static void scan_for_empty_cpusets(const
struct list_head queue;
struct cgroup *cont;
nodemask_t oldmems;
+ cpumask_t oldcpus;
INIT_LIST_HEAD(&queue);
@@ -1876,6 +1915,7 @@ static void scan_for_empty_cpusets(const
continue;
oldmems = cp->mems_allowed;
+ oldcpus = cp->cpus_allowed;
/* Remove offline cpus and mems from this cpuset. */
mutex_lock(&callback_mutex);
@@ -1884,6 +1924,12 @@ static void scan_for_empty_cpusets(const
node_states[N_HIGH_MEMORY]);
mutex_unlock(&callback_mutex);
+ if (is_sched_load_balance(cp)) {
+ if (cpus_empty(cp->cpus_allowed) &&
+ !cpus_empty(oldcpus))
+ cpusets_rd_lv[cp->relax_domain_level]--;
+ }
+
/* Move tasks from the empty cpuset to a parent */
if (cpus_empty(cp->cpus_allowed) ||
nodes_empty(cp->mems_allowed))
--
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