This patch prevents the 'sched_load_balance' flag from being fippled off when DL tasks are present in a CPUset. Otherwise we end up with the DL tasks using CPUs belonging to different root domains, something that breaks the mathematical model behind DL bandwidth management.
For example on a 4 core system CPUset "set1" has been created and CPUs 0 and 1 assigned to it. A DL task has also been spun off. By default the DL task can use all the CPUs in the default CPUset. If we set the base CPUset's cpuset.sched_load_balance to '0', CPU 0 and 1 are added to a newly created root domain while CPU 2 and 3 endup in the default root domain. But the DL task is still part of the base CPUset and as such can use CPUs 0 to 3, spanning at the same time more than one root domain. Signed-off-by: Mathieu Poirier <[email protected]> --- kernel/cgroup/cpuset.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 82 insertions(+) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index f6d1e485dc2d..18df143b4013 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -447,6 +447,85 @@ static void free_trial_cpuset(struct cpuset *trial) kfree(trial); } +static bool cpuset_has_dl_tasks(struct cpuset *cs) +{ + bool dl_tasks = false; + struct css_task_iter it; + struct task_struct *task; + + /* Go through each task in @cs looking for a DL task */ + css_task_iter_start(&cs->css, &it); + + while (!dl_tasks && (task = css_task_iter_next(&it))) { + if (dl_task(task)) + dl_tasks = true; + } + + css_task_iter_end(&it); + + return dl_tasks; +} + +/* + * Assumes RCU read lock and cpuset_mutex are held. + */ +static int validate_dl_change(struct cpuset *cur, struct cpuset *trial) +{ + bool populated = false, dl_tasks = false; + int ret = -EBUSY; + struct cgroup_subsys_state *pos_css; + struct cpuset *cs; + + /* + * The cpuset.sched_load_balance flag is flipped off on + * the current cpuset. + */ + if (is_sched_load_balance(cur) && + !is_sched_load_balance(trial)) { + /* See if at least one descendant cpuset is populated */ + cpuset_for_each_descendant_pre(cs, pos_css, cur) { + /* Skip over ourselve */ + if (cs == cur) + continue; + + /* Empty cpusets are of no interest */ + if (cpumask_empty(cs->cpus_allowed)) { + pos_css = css_rightmost_descendant(pos_css); + continue; + } + + /* + * @cur has at least one children and CPUs have been + * assigned to it - there is no need to go further. + */ + populated = true; + break; + } + + dl_tasks = cpuset_has_dl_tasks(cur); + + /* + * This CPUset has a children that is populated by (at least) + * one CPU. When the sched_load_balance flag gets flipped off + * it will create a new root domain for the children CPUset, + * and that new root domain will include the CPUs assigned to + * the CPUset. + * + * Since the tasks in the current CPUset have not been assigned + * to the children CPUset they will simply stay here and use + * all the CPUs available in this set. For DL tasks this can't + * be allowed since they will be executing on CPUs associated to + * more than one root domains. + */ + if (populated && dl_tasks) + goto out; + } + + ret = 0; +out: + return ret; +} + /* * validate_change() - Used to validate that any proposed cpuset change * follows the structural rules for cpusets. @@ -481,6 +560,9 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial) if (!is_cpuset_subset(c, trial)) goto out; + if (validate_dl_change(cur, trial)) + goto out; + /* Remaining checks don't apply to root cpuset */ ret = 0; if (cur == &top_cpuset) -- 2.7.4
