Messages in this thread Patch in this message | | | Date | Thu, 17 Jul 2008 16:07:44 +0800 | From | Li Zefan <> | Subject | [RFC] [PATCH] cpuset: fix wrong calculation of relax domain level |
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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@cn.fujitsu.com> Signed-off-by: Li Zefan <lizf@cn.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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