A cpuset partition is a collection of cpusets with a partition root and its descendants from that root downward excluding any cpusets that are part of other partitions. A partition has exclusive access to a set of CPUs granted to it. Other cpusets outside of a partition cannot use any CPUs in that set.

Currently, creation of partitions requires a hierarchical CPUs distribution model where the parent of a partition root has to be a partition root itself. Hence all the partition roots have to be clustered around the cgroup root.

To enable the creation of a remote partition down in the hierarchy without a parental partition root, we need a way to reserve the CPUs that will be used in a remote partition. Introduce a new root-only "cpuset.cpus.reserve" control file in the top cpuset for this particular purpose.

By default, the new "cpuset.cpus.reserve" control file will track the subparts_cpus cpumask in the top cpuset. By writing into this new control file, however, we can reserve additional CPUs that can be used in a remote partition. Any CPUs that are in "cpuset.cpus.reserve" will have to be removed from the effective_cpus of all the cpusets that are not part of that valid partitions.

The prefix "+" and "-" can be used to indicate the addition to or the subtraction from the existing CPUs in "cpuset.cpus.reserve". A single "-" character indicate the deletion of all the free reserve CPUs not allocated to any existing partition.

Signed-off-by: Waiman Long longman@redhat.com --- kernel/cgroup/cpuset.c | 253 ++++++++++++++++++++++++++++++++++++++--- 1 file changed, 239 insertions(+), 14 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 8604c919e1e4..69abe95a9969 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -208,7 +208,33 @@ struct cpuset { struct cgroup_file partition_file; };

-static cpumask_var_t cs_tmp_cpus; /* Temp cpumask for partition */ +/* + * Reserved CPUs for partitions. + * + * By default, CPUs used in partitions are tracked in the parent's + * subparts_cpus mask following a hierarchical CPUs distribution model. + * To enable the creation of a remote partition down in the hierarchy + * without a parental partition root, one can write directly to + * cpuset.cpus.reserve in the root cgroup to allocate more CPUs that can + * be used by remote partitions. Removal of existing reserved CPUs may + * also cause some existing partitions to become invalid. + * + * All the cpumasks below should only be used with cpuset_mutex held. + * Modification of cs_reserve_cpus & cs_free_reserve_cpus also requires + * holding the callback_lock. + * + * Relationship among cs_reserve_cpus, cs_free_reserve_cpus and + * top_cpuset.subparts_cpus are: + * + * top_cpuset.subparts_cpus ⊆ cs_reserve_cpus + * cs_free_reserve_cpus ⊆ cs_reserve_cpus + * top_cpuset.subparts_cpus ∩ cs_free_reserve_cpus = ∅ + * cs_reserve_cpus - cs_free_reserve_cpus - top_cpuset.subparts_cpus + * = CPUs dedicated to remote partitions + */ +static cpumask_var_t cs_reserve_cpus; /* Reserved CPUs */ +static cpumask_var_t cs_free_reserve_cpus; /* Unallocated reserved CPUs */ +static cpumask_var_t cs_tmp_cpus; /* Temp cpumask for partition */

/* * Partition root states: @@ -1202,13 +1228,13 @@ static void rebuild_sched_domains_locked(void) * should be the same as the active CPUs, so checking only top_cpuset * is enough to detect racing CPU offlines. */ - if (!top_cpuset.nr_subparts_cpus && + if (cpumask_empty(cs_reserve_cpus) && !cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask)) return;

/* * With subpartition CPUs, however, the effective CPUs of a partition - * root should be only a subset of the active CPUs. Since a CPU in any + * root should only be a subset of the active CPUs. Since a CPU in any * partition root could be offlined, all must be checked. */ if (top_cpuset.nr_subparts_cpus) { @@ -1275,7 +1301,7 @@ static void update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus) */ if ((task->flags & PF_KTHREAD) && kthread_is_per_cpu(task)) continue; - cpumask_andnot(new_cpus, possible_mask, cs->subparts_cpus); + cpumask_andnot(new_cpus, possible_mask, cs_reserve_cpus); } else { cpumask_and(new_cpus, possible_mask, cs->effective_cpus); } @@ -1406,6 +1432,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd, int deleting; /* Moving cpus from subparts_cpus to effective_cpus */ int old_prs, new_prs; int part_error = PERR_NONE; /* Partition error? */ + bool update_reserve = (parent == &top_cpuset);

lockdep_assert_held(&cpuset_mutex);

@@ -1576,7 +1603,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd, }

/* - * Change the parent's subparts_cpus. + * Change the parent's subparts_cpus and maybe cs_reserve_cpus. * Newly added CPUs will be removed from effective_cpus and * newly deleted ones will be added back to effective_cpus. */ @@ -1586,10 +1613,25 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd, parent->subparts_cpus, tmp->addmask); cpumask_andnot(parent->effective_cpus, parent->effective_cpus, tmp->addmask); + if (update_reserve) { + cpumask_or(cs_reserve_cpus, + cs_reserve_cpus, tmp->addmask); + cpumask_andnot(cs_free_reserve_cpus, + cs_free_reserve_cpus, tmp->addmask); + } } if (deleting) { cpumask_andnot(parent->subparts_cpus, parent->subparts_cpus, tmp->delmask); + /* + * The automatic cpu reservation of adjacent partition + * won't add back the deleted CPUs to cs_free_reserve_cpus. + * Instead, they are returned back to effective_cpus of top + * cpuset. + */ + if (update_reserve) + cpumask_andnot(cs_reserve_cpus, + cs_reserve_cpus, tmp->delmask); /* * Some of the CPUs in subparts_cpus might have been offlined. */ @@ -1783,6 +1825,8 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,

if (need_rebuild_sched_domains) rebuild_sched_domains_locked(); + + return; }

/** @@ -1955,6 +1999,167 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs, return 0; }

+/** + * update_reserve_cpumask - update cs_reserve_cpus + * @trialcs: trial cpuset + * @buf: buffer of cpu numbers written to this cpuset + * Return: 0 if successful, < 0 if error + */ +static int update_reserve_cpumask(struct cpuset *trialcs, const char *buf) +{ + struct cgroup_subsys_state *css; + struct cpuset *cs; + bool adding, deleting; + struct tmpmasks tmp; + + adding = deleting = false; + if (*buf == '+') { + adding = true; + buf++; + } else if (*buf == '-') { + deleting = true; + buf++; + } + + if (!*buf) { + if (adding) + return -EINVAL; + + if (deleting) { + if (cpumask_empty(cs_free_reserve_cpus)) + return 0; + cpumask_copy(trialcs->cpus_allowed, cs_free_reserve_cpus); + } else { + cpumask_clear(trialcs->cpus_allowed); + } + } else { + int retval = cpulist_parse(buf, trialcs->cpus_allowed); + + if (retval < 0) + return retval; + } + + if (!adding && !deleting && + cpumask_equal(trialcs->cpus_allowed, cs_reserve_cpus)) + return 0; + + /* Preserve trialcs->cpus_allowed for now */ + init_tmpmasks(&tmp, NULL, trialcs->subparts_cpus, + trialcs->effective_cpus); + + /* + * Compute the addition and removal of CPUs to/from cs_reserve_cpus + */ + if (!adding && !deleting) { + adding = cpumask_andnot(tmp.addmask, trialcs->cpus_allowed, + cs_reserve_cpus); + deleting = cpumask_andnot(tmp.delmask, cs_reserve_cpus, + trialcs->cpus_allowed); + } else if (adding) { + adding = cpumask_andnot(tmp.addmask, + trialcs->cpus_allowed, cs_reserve_cpus); + cpumask_or(trialcs->cpus_allowed, cs_reserve_cpus, tmp.addmask); + } else { /* deleting */ + deleting = cpumask_and(tmp.delmask, + trialcs->cpus_allowed, cs_reserve_cpus); + cpumask_andnot(trialcs->cpus_allowed, cs_reserve_cpus, tmp.delmask); + } + + if (!adding && !deleting) + return 0; + + /* + * Invalidate remote partitions if necessary + */ + if (deleting) { + /* TODO */ + } + + /* + * Cannot use up all the CPUs in top_cpuset.effective_cpus + */ + if (!deleting && adding && + cpumask_subset(top_cpuset.effective_cpus, tmp.addmask)) + return -EINVAL; + + spin_lock_irq(&callback_lock); + /* + * Update top_cpuset.effective_cpus, cs_reserve_cpus & + * cs_free_reserve_cpus. + */ + if (adding) + cpumask_or(cs_free_reserve_cpus, cs_free_reserve_cpus, + tmp.addmask); + cpumask_copy(cs_reserve_cpus, trialcs->cpus_allowed); + cpumask_andnot(top_cpuset.effective_cpus, + cpu_active_mask, cs_reserve_cpus); + + /* + * Remove CPUs from cs_free_reserve_cpus first. Anything left + * means some partitions has to be made invalid. + */ + if (deleting & cpumask_and(cs_tmp_cpus, cs_free_reserve_cpus, + tmp.delmask)) { + cpumask_andnot(cs_free_reserve_cpus, cs_free_reserve_cpus, + cs_tmp_cpus); + deleting = cpumask_andnot(tmp.delmask, tmp.delmask, + cs_tmp_cpus); + } + spin_unlock_irq(&callback_lock); + + /* + * Invalidate some adjacent partitions under top cpuset, if necessary + */ + if (deleting && cpumask_and(cs_tmp_cpus, tmp.delmask, + top_cpuset.subparts_cpus)) { + struct cgroup_subsys_state *css; + struct cpuset *cp; + + /* + * Temporarily save the remaining CPUs to be deleted in + * trialcs->cpus_allowed to be restored back to tmp.delmask + * later. + */ + deleting = cpumask_andnot(trialcs->cpus_allowed, tmp.delmask, + cs_tmp_cpus); + rcu_read_lock(); + cpuset_for_each_child(cp, css, &top_cpuset) + if (is_partition_valid(cp) && + cpumask_intersects(cs_tmp_cpus, cp->cpus_allowed)) { + rcu_read_unlock(); + update_parent_subparts_cpumask(cp, partcmd_invalidate, NULL, &tmp); + rcu_read_lock(); + } + rcu_read_unlock(); + if (deleting) + cpumask_copy(tmp.delmask, trialcs->cpus_allowed); + } + + /* Can now use all of trialcs */ + init_tmpmasks(&tmp, trialcs->cpus_allowed, trialcs->subparts_cpus, + trialcs->effective_cpus); + + /* + * Update effective_cpus of all descendants that are not in + * partitions and rebuild sched domaiins. + */ + rcu_read_lock(); + cpuset_for_each_child(cs, css, &top_cpuset) { + compute_effective_cpumask(tmp.new_cpus, cs, &top_cpuset); + if (cpumask_equal(tmp.new_cpus, cs->effective_cpus)) + continue; + if (!css_tryget_online(&cs->css)) + continue; + rcu_read_unlock(); + update_cpumasks_hier(cs, &tmp, false); + rcu_read_lock(); + css_put(&cs->css); + } + rcu_read_unlock(); + rebuild_sched_domains_locked(); + return 0; +} + /* * Migrate memory region from one set of nodes to another. This is * performed asynchronously as it can be called from process migration path @@ -2743,6 +2948,7 @@ typedef enum { FILE_EFFECTIVE_CPULIST, FILE_EFFECTIVE_MEMLIST, FILE_SUBPARTS_CPULIST, + FILE_RESERVE_CPULIST, FILE_CPU_EXCLUSIVE, FILE_MEM_EXCLUSIVE, FILE_MEM_HARDWALL, @@ -2880,6 +3086,9 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of, case FILE_CPULIST: retval = update_cpumask(cs, trialcs, buf); break; + case FILE_RESERVE_CPULIST: + retval = update_reserve_cpumask(trialcs, buf); + break; case FILE_MEMLIST: retval = update_nodemask(cs, trialcs, buf); break; @@ -2927,6 +3136,9 @@ static int cpuset_common_seq_show(struct seq_file *sf, void *v) case FILE_EFFECTIVE_MEMLIST: seq_printf(sf, "%*pbl\n", nodemask_pr_args(&cs->effective_mems)); break; + case FILE_RESERVE_CPULIST: + seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs_reserve_cpus)); + break; case FILE_SUBPARTS_CPULIST: seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->subparts_cpus)); break; @@ -3200,6 +3412,14 @@ static struct cftype dfl_files[] = { .file_offset = offsetof(struct cpuset, partition_file), },

+ { + .name = "cpus.reserve", + .seq_show = cpuset_common_seq_show, + .write = cpuset_write_resmask, + .private = FILE_RESERVE_CPULIST, + .flags = CFTYPE_ONLY_ON_ROOT, + }, + { .name = "cpus.subpartitions", .seq_show = cpuset_common_seq_show, @@ -3510,6 +3730,8 @@ int __init cpuset_init(void) BUG_ON(!alloc_cpumask_var(&top_cpuset.effective_cpus, GFP_KERNEL)); BUG_ON(!zalloc_cpumask_var(&top_cpuset.subparts_cpus, GFP_KERNEL)); BUG_ON(!zalloc_cpumask_var(&cs_tmp_cpus, GFP_KERNEL)); + BUG_ON(!zalloc_cpumask_var(&cs_reserve_cpus, GFP_KERNEL)); + BUG_ON(!zalloc_cpumask_var(&cs_free_reserve_cpus, GFP_KERNEL));

cpumask_setall(top_cpuset.cpus_allowed); nodes_setall(top_cpuset.mems_allowed); @@ -3788,10 +4010,10 @@ static void cpuset_hotplug_workfn(struct work_struct *work) mems_updated = !nodes_equal(top_cpuset.effective_mems, new_mems);

/* - * In the rare case that hotplug removes all the cpus in subparts_cpus, + * In the rare case that hotplug removes all the reserve cpus, * we assumed that cpus are updated. */ - if (!cpus_updated && top_cpuset.nr_subparts_cpus) + if (!cpus_updated && !cpumask_empty(cs_reserve_cpus)) cpus_updated = true;

/* synchronize cpus_allowed to cpu_active_mask */ @@ -3801,18 +4023,21 @@ static void cpuset_hotplug_workfn(struct work_struct *work) cpumask_copy(top_cpuset.cpus_allowed, &new_cpus); /* * Make sure that CPUs allocated to child partitions - * do not show up in effective_cpus. If no CPU is left, - * we clear the subparts_cpus & let the child partitions - * fight for the CPUs again. + * do not show up in top_cpuset's effective_cpus. In the + * unlikely event tht no effective CPU is left in top_cpuset, + * we clear all the reserve cpus and let the non-remote child + * partitions fight for the CPUs again. */ - if (top_cpuset.nr_subparts_cpus) { - if (cpumask_subset(&new_cpus, - top_cpuset.subparts_cpus)) { + if (!cpumask_empty(cs_reserve_cpus)) { + + if (cpumask_subset(&new_cpus, cs_reserve_cpus)) { top_cpuset.nr_subparts_cpus = 0; cpumask_clear(top_cpuset.subparts_cpus); + cpumask_clear(cs_free_reserve_cpus); + cpumask_clear(cs_reserve_cpus); } else { cpumask_andnot(&new_cpus, &new_cpus, - top_cpuset.subparts_cpus); + cs_reserve_cpus); } } cpumask_copy(top_cpuset.effective_cpus, &new_cpus);