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Subject[GIT PULL] scheduler changes for v3.6
Linus,

Please pull the latest sched-core-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-core-for-linus

HEAD: 8323f26ce3425460769605a6aece7a174edaa7d1 sched: Fix race in task_group()

The biggest change is a performance improvement on SMP systems:

| 4 socket 40 core + SMT Westmere box, single 30 sec tbench
| runs, higher is better:
|
| clients 1 2 4 8 16 32 64 128
|..........................................................................
| pre 30 41 118 645 3769 6214 12233 14312
| post 299 603 1211 2418 4697 6847 11606 14557
|
| A nice increase in performance.

which speedup is particularly noticeable on heavily interacting
few-tasks workloads, so the changes should help desktop-style
Xorg workloads and interactivity as well, on multi-core CPUs.

There are also cpuset suspend behavior fixes/restructuring and
various smaller tweaks.

( I had to rebase the pending scheduler tree recently, as the
work in progress NUMA scheduling changes from Peter Zijlstra
were still too raw for v3.6. This was hopefully a rare,
one-off event. )

Thanks,

Ingo

------------------>
Mike Galbraith (1):
sched: Improve scalability via 'CPU buddies', which withstand random perturbations
Peter Zijlstra (2):
sched/x86: Remove broken power estimation
sched: Fix race in task_group()

Prashanth Nageshappa (2):
sched: Reorder 'struct lb_env' members to reduce its size
sched: Reset loop counters if all tasks are pinned and we need to redo load balance

Srivatsa S. Bhat (4):
CPU hotplug, cpusets, suspend: Don't modify cpusets during suspend/resume
cpusets, hotplug: Implement cpuset tree traversal in a helper function
cpusets, hotplug: Restructure functions that are invoked during hotplug
cpusets: Remove/update outdated comments

Srivatsa Vaddagiri (1):
sched: Improve balance_cpu() to consider other cpus in its group as target of (pinned) task


arch/x86/kernel/cpu/Makefile | 2 +-
arch/x86/kernel/cpu/sched.c | 55 ------------------
include/linux/cpuset.h | 4 +-
include/linux/init_task.h | 12 +++-
include/linux/sched.h | 6 +-
kernel/cpuset.c | 130 ++++++++++++++++++++++++++++++------------
kernel/sched/core.c | 92 +++++++++++++++++++++++++++---
kernel/sched/fair.c | 113 +++++++++++++++++++++++++++---------
kernel/sched/sched.h | 23 ++++----
9 files changed, 291 insertions(+), 146 deletions(-)
delete mode 100644 arch/x86/kernel/cpu/sched.c
diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
index 6ab6aa2..c598126 100644
--- a/arch/x86/kernel/cpu/Makefile
+++ b/arch/x86/kernel/cpu/Makefile
@@ -14,7 +14,7 @@ CFLAGS_common.o := $(nostackp)

obj-y := intel_cacheinfo.o scattered.o topology.o
obj-y += proc.o capflags.o powerflags.o common.o
-obj-y += vmware.o hypervisor.o sched.o mshyperv.o
+obj-y += vmware.o hypervisor.o mshyperv.o
obj-y += rdrand.o
obj-y += match.o

diff --git a/arch/x86/kernel/cpu/sched.c b/arch/x86/kernel/cpu/sched.c
deleted file mode 100644
index a640ae5..0000000
--- a/arch/x86/kernel/cpu/sched.c
+++ /dev/null
@@ -1,55 +0,0 @@
-#include <linux/sched.h>
-#include <linux/math64.h>
-#include <linux/percpu.h>
-#include <linux/irqflags.h>
-
-#include <asm/cpufeature.h>
-#include <asm/processor.h>
-
-#ifdef CONFIG_SMP
-
-static DEFINE_PER_CPU(struct aperfmperf, old_perf_sched);
-
-static unsigned long scale_aperfmperf(void)
-{
- struct aperfmperf val, *old = &__get_cpu_var(old_perf_sched);
- unsigned long ratio, flags;
-
- local_irq_save(flags);
- get_aperfmperf(&val);
- local_irq_restore(flags);
-
- ratio = calc_aperfmperf_ratio(old, &val);
- *old = val;
-
- return ratio;
-}
-
-unsigned long arch_scale_freq_power(struct sched_domain *sd, int cpu)
-{
- /*
- * do aperf/mperf on the cpu level because it includes things
- * like turbo mode, which are relevant to full cores.
- */
- if (boot_cpu_has(X86_FEATURE_APERFMPERF))
- return scale_aperfmperf();
-
- /*
- * maybe have something cpufreq here
- */
-
- return default_scale_freq_power(sd, cpu);
-}
-
-unsigned long arch_scale_smt_power(struct sched_domain *sd, int cpu)
-{
- /*
- * aperf/mperf already includes the smt gain
- */
- if (boot_cpu_has(X86_FEATURE_APERFMPERF))
- return SCHED_LOAD_SCALE;
-
- return default_scale_smt_power(sd, cpu);
-}
-
-#endif
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 668f66b..838320f 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -20,7 +20,7 @@ extern int number_of_cpusets; /* How many cpusets are defined in system? */

extern int cpuset_init(void);
extern void cpuset_init_smp(void);
-extern void cpuset_update_active_cpus(void);
+extern void cpuset_update_active_cpus(bool cpu_online);
extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
extern void cpuset_cpus_allowed_fallback(struct task_struct *p);
extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
@@ -124,7 +124,7 @@ static inline void set_mems_allowed(nodemask_t nodemask)
static inline int cpuset_init(void) { return 0; }
static inline void cpuset_init_smp(void) {}

-static inline void cpuset_update_active_cpus(void)
+static inline void cpuset_update_active_cpus(bool cpu_online)
{
partition_sched_domains(1, NULL, NULL);
}
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 9e65eff..b806b82 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -123,8 +123,17 @@ extern struct group_info init_groups;

extern struct cred init_cred;

+extern struct task_group root_task_group;
+
+#ifdef CONFIG_CGROUP_SCHED
+# define INIT_CGROUP_SCHED(tsk) \
+ .sched_task_group = &root_task_group,
+#else
+# define INIT_CGROUP_SCHED(tsk)
+#endif
+
#ifdef CONFIG_PERF_EVENTS
-# define INIT_PERF_EVENTS(tsk) \
+# define INIT_PERF_EVENTS(tsk) \
.perf_event_mutex = \
__MUTEX_INITIALIZER(tsk.perf_event_mutex), \
.perf_event_list = LIST_HEAD_INIT(tsk.perf_event_list),
@@ -161,6 +170,7 @@ extern struct cred init_cred;
}, \
.tasks = LIST_HEAD_INIT(tsk.tasks), \
INIT_PUSHABLE_TASKS(tsk) \
+ INIT_CGROUP_SCHED(tsk) \
.ptraced = LIST_HEAD_INIT(tsk.ptraced), \
.ptrace_entry = LIST_HEAD_INIT(tsk.ptrace_entry), \
.real_parent = &tsk, \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4a1f493..fd9436a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -949,6 +949,7 @@ struct sched_domain {
unsigned int smt_gain;
int flags; /* See SD_* */
int level;
+ int idle_buddy; /* cpu assigned to select_idle_sibling() */

/* Runtime fields. */
unsigned long last_balance; /* init to jiffies. units in jiffies */
@@ -1244,6 +1245,9 @@ struct task_struct {
const struct sched_class *sched_class;
struct sched_entity se;
struct sched_rt_entity rt;
+#ifdef CONFIG_CGROUP_SCHED
+ struct task_group *sched_task_group;
+#endif

#ifdef CONFIG_PREEMPT_NOTIFIERS
/* list of struct preempt_notifier: */
@@ -2723,7 +2727,7 @@ extern int sched_group_set_rt_period(struct task_group *tg,
extern long sched_group_rt_period(struct task_group *tg);
extern int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk);
#endif
-#endif
+#endif /* CONFIG_CGROUP_SCHED */

extern int task_can_switch_user(struct user_struct *up,
struct task_struct *tsk);
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 8c8bd65..f33c715 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -147,6 +147,12 @@ typedef enum {
CS_SPREAD_SLAB,
} cpuset_flagbits_t;

+/* the type of hotplug event */
+enum hotplug_event {
+ CPUSET_CPU_OFFLINE,
+ CPUSET_MEM_OFFLINE,
+};
+
/* convenient tests for these bits */
static inline int is_cpu_exclusive(const struct cpuset *cs)
{
@@ -1990,8 +1996,36 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
}

/*
- * Walk the specified cpuset subtree and look for empty cpusets.
- * The tasks of such cpuset must be moved to a parent cpuset.
+ * Helper function to traverse cpusets.
+ * It can be used to walk the cpuset tree from top to bottom, completing
+ * one layer before dropping down to the next (thus always processing a
+ * node before any of its children).
+ */
+static struct cpuset *cpuset_next(struct list_head *queue)
+{
+ struct cpuset *cp;
+ struct cpuset *child; /* scans child cpusets of cp */
+ struct cgroup *cont;
+
+ if (list_empty(queue))
+ return NULL;
+
+ cp = list_first_entry(queue, struct cpuset, stack_list);
+ list_del(queue->next);
+ list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
+ child = cgroup_cs(cont);
+ list_add_tail(&child->stack_list, queue);
+ }
+
+ return cp;
+}
+
+
+/*
+ * Walk the specified cpuset subtree upon a hotplug operation (CPU/Memory
+ * online/offline) and update the cpusets accordingly.
+ * For regular CPU/Mem hotplug, look for empty cpusets; the tasks of such
+ * cpuset must be moved to a parent cpuset.
*
* Called with cgroup_mutex held. We take callback_mutex to modify
* cpus_allowed and mems_allowed.
@@ -2000,50 +2034,61 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
* before dropping down to the next. It always processes a node before
* any of its children.
*
- * For now, since we lack memory hot unplug, we'll never see a cpuset
- * that has tasks along with an empty 'mems'. But if we did see such
- * a cpuset, we'd handle it just like we do if its 'cpus' was empty.
+ * In the case of memory hot-unplug, it will remove nodes from N_HIGH_MEMORY
+ * if all present pages from a node are offlined.
*/
-static void scan_for_empty_cpusets(struct cpuset *root)
+static void
+scan_cpusets_upon_hotplug(struct cpuset *root, enum hotplug_event event)
{
LIST_HEAD(queue);
- struct cpuset *cp; /* scans cpusets being updated */
- struct cpuset *child; /* scans child cpusets of cp */
- struct cgroup *cont;
+ struct cpuset *cp; /* scans cpusets being updated */
static nodemask_t oldmems; /* protected by cgroup_mutex */

list_add_tail((struct list_head *)&root->stack_list, &queue);

- while (!list_empty(&queue)) {
- cp = list_first_entry(&queue, struct cpuset, stack_list);
- list_del(queue.next);
- list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
- child = cgroup_cs(cont);
- list_add_tail(&child->stack_list, &queue);
+ switch (event) {
+ case CPUSET_CPU_OFFLINE:
+ while ((cp = cpuset_next(&queue)) != NULL) {
+
+ /* Continue past cpusets with all cpus online */
+ if (cpumask_subset(cp->cpus_allowed, cpu_active_mask))
+ continue;
+
+ /* Remove offline cpus from this cpuset. */
+ mutex_lock(&callback_mutex);
+ cpumask_and(cp->cpus_allowed, cp->cpus_allowed,
+ cpu_active_mask);
+ mutex_unlock(&callback_mutex);
+
+ /* Move tasks from the empty cpuset to a parent */
+ if (cpumask_empty(cp->cpus_allowed))
+ remove_tasks_in_empty_cpuset(cp);
+ else
+ update_tasks_cpumask(cp, NULL);
}
+ break;

- /* Continue past cpusets with all cpus, mems online */
- if (cpumask_subset(cp->cpus_allowed, cpu_active_mask) &&
- nodes_subset(cp->mems_allowed, node_states[N_HIGH_MEMORY]))
- continue;
+ case CPUSET_MEM_OFFLINE:
+ while ((cp = cpuset_next(&queue)) != NULL) {

- oldmems = cp->mems_allowed;
+ /* Continue past cpusets with all mems online */
+ if (nodes_subset(cp->mems_allowed,
+ node_states[N_HIGH_MEMORY]))
+ continue;

- /* Remove offline cpus and mems from this cpuset. */
- mutex_lock(&callback_mutex);
- cpumask_and(cp->cpus_allowed, cp->cpus_allowed,
- cpu_active_mask);
- nodes_and(cp->mems_allowed, cp->mems_allowed,
+ oldmems = cp->mems_allowed;
+
+ /* Remove offline mems from this cpuset. */
+ mutex_lock(&callback_mutex);
+ nodes_and(cp->mems_allowed, cp->mems_allowed,
node_states[N_HIGH_MEMORY]);
- mutex_unlock(&callback_mutex);
+ mutex_unlock(&callback_mutex);

- /* Move tasks from the empty cpuset to a parent */
- if (cpumask_empty(cp->cpus_allowed) ||
- nodes_empty(cp->mems_allowed))
- remove_tasks_in_empty_cpuset(cp);
- else {
- update_tasks_cpumask(cp, NULL);
- update_tasks_nodemask(cp, &oldmems, NULL);
+ /* Move tasks from the empty cpuset to a parent */
+ if (nodes_empty(cp->mems_allowed))
+ remove_tasks_in_empty_cpuset(cp);
+ else
+ update_tasks_nodemask(cp, &oldmems, NULL);
}
}
}
@@ -2054,13 +2099,19 @@ static void scan_for_empty_cpusets(struct cpuset *root)
* (of no affect) on systems that are actively using CPU hotplug
* but making no active use of cpusets.
*
+ * The only exception to this is suspend/resume, where we don't
+ * modify cpusets at all.
+ *
* This routine ensures that top_cpuset.cpus_allowed tracks
* cpu_active_mask on each CPU hotplug (cpuhp) event.
*
* Called within get_online_cpus(). Needs to call cgroup_lock()
* before calling generate_sched_domains().
+ *
+ * @cpu_online: Indicates whether this is a CPU online event (true) or
+ * a CPU offline event (false).
*/
-void cpuset_update_active_cpus(void)
+void cpuset_update_active_cpus(bool cpu_online)
{
struct sched_domain_attr *attr;
cpumask_var_t *doms;
@@ -2070,7 +2121,10 @@ void cpuset_update_active_cpus(void)
mutex_lock(&callback_mutex);
cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
mutex_unlock(&callback_mutex);
- scan_for_empty_cpusets(&top_cpuset);
+
+ if (!cpu_online)
+ scan_cpusets_upon_hotplug(&top_cpuset, CPUSET_CPU_OFFLINE);
+
ndoms = generate_sched_domains(&doms, &attr);
cgroup_unlock();

@@ -2082,7 +2136,7 @@ void cpuset_update_active_cpus(void)
/*
* Keep top_cpuset.mems_allowed tracking node_states[N_HIGH_MEMORY].
* Call this routine anytime after node_states[N_HIGH_MEMORY] changes.
- * See also the previous routine cpuset_track_online_cpus().
+ * See cpuset_update_active_cpus() for CPU hotplug handling.
*/
static int cpuset_track_online_nodes(struct notifier_block *self,
unsigned long action, void *arg)
@@ -2101,9 +2155,9 @@ static int cpuset_track_online_nodes(struct notifier_block *self,
case MEM_OFFLINE:
/*
* needn't update top_cpuset.mems_allowed explicitly because
- * scan_for_empty_cpusets() will update it.
+ * scan_cpusets_upon_hotplug() will update it.
*/
- scan_for_empty_cpusets(&top_cpuset);
+ scan_cpusets_upon_hotplug(&top_cpuset, CPUSET_MEM_OFFLINE);
break;
default:
break;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 468bdd4..5d011ef 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1096,7 +1096,7 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
* a task's CPU. ->pi_lock for waking tasks, rq->lock for runnable tasks.
*
* sched_move_task() holds both and thus holding either pins the cgroup,
- * see set_task_rq().
+ * see task_group().
*
* Furthermore, all task_rq users should acquire both locks, see
* task_rq_lock().
@@ -6024,6 +6024,11 @@ static void destroy_sched_domains(struct sched_domain *sd, int cpu)
* SD_SHARE_PKG_RESOURCE set (Last Level Cache Domain) for this
* allows us to avoid some pointer chasing select_idle_sibling().
*
+ * Iterate domains and sched_groups downward, assigning CPUs to be
+ * select_idle_sibling() hw buddy. Cross-wiring hw makes bouncing
+ * due to random perturbation self canceling, ie sw buddies pull
+ * their counterpart to their CPU's hw counterpart.
+ *
* Also keep a unique ID per domain (we use the first cpu number in
* the cpumask of the domain), this allows us to quickly tell if
* two cpus are in the same cache domain, see cpus_share_cache().
@@ -6037,8 +6042,40 @@ static void update_top_cache_domain(int cpu)
int id = cpu;

sd = highest_flag_domain(cpu, SD_SHARE_PKG_RESOURCES);
- if (sd)
+ if (sd) {
+ struct sched_domain *tmp = sd;
+ struct sched_group *sg, *prev;
+ bool right;
+
+ /*
+ * Traverse to first CPU in group, and count hops
+ * to cpu from there, switching direction on each
+ * hop, never ever pointing the last CPU rightward.
+ */
+ do {
+ id = cpumask_first(sched_domain_span(tmp));
+ prev = sg = tmp->groups;
+ right = 1;
+
+ while (cpumask_first(sched_group_cpus(sg)) != id)
+ sg = sg->next;
+
+ while (!cpumask_test_cpu(cpu, sched_group_cpus(sg))) {
+ prev = sg;
+ sg = sg->next;
+ right = !right;
+ }
+
+ /* A CPU went down, never point back to domain start. */
+ if (right && cpumask_first(sched_group_cpus(sg->next)) == id)
+ right = false;
+
+ sg = right ? sg->next : prev;
+ tmp->idle_buddy = cpumask_first(sched_group_cpus(sg));
+ } while ((tmp = tmp->child));
+
id = cpumask_first(sched_domain_span(sd));
+ }

rcu_assign_pointer(per_cpu(sd_llc, cpu), sd);
per_cpu(sd_llc_id, cpu) = id;
@@ -7097,34 +7134,66 @@ match2:
mutex_unlock(&sched_domains_mutex);
}

+static int num_cpus_frozen; /* used to mark begin/end of suspend/resume */
+
/*
* Update cpusets according to cpu_active mask. If cpusets are
* disabled, cpuset_update_active_cpus() becomes a simple wrapper
* around partition_sched_domains().
+ *
+ * If we come here as part of a suspend/resume, don't touch cpusets because we
+ * want to restore it back to its original state upon resume anyway.
*/
static int cpuset_cpu_active(struct notifier_block *nfb, unsigned long action,
void *hcpu)
{
- switch (action & ~CPU_TASKS_FROZEN) {
+ switch (action) {
+ case CPU_ONLINE_FROZEN:
+ case CPU_DOWN_FAILED_FROZEN:
+
+ /*
+ * num_cpus_frozen tracks how many CPUs are involved in suspend
+ * resume sequence. As long as this is not the last online
+ * operation in the resume sequence, just build a single sched
+ * domain, ignoring cpusets.
+ */
+ num_cpus_frozen--;
+ if (likely(num_cpus_frozen)) {
+ partition_sched_domains(1, NULL, NULL);
+ break;
+ }
+
+ /*
+ * This is the last CPU online operation. So fall through and
+ * restore the original sched domains by considering the
+ * cpuset configurations.
+ */
+
case CPU_ONLINE:
case CPU_DOWN_FAILED:
- cpuset_update_active_cpus();
- return NOTIFY_OK;
+ cpuset_update_active_cpus(true);
+ break;
default:
return NOTIFY_DONE;
}
+ return NOTIFY_OK;
}

static int cpuset_cpu_inactive(struct notifier_block *nfb, unsigned long action,
void *hcpu)
{
- switch (action & ~CPU_TASKS_FROZEN) {
+ switch (action) {
case CPU_DOWN_PREPARE:
- cpuset_update_active_cpus();
- return NOTIFY_OK;
+ cpuset_update_active_cpus(false);
+ break;
+ case CPU_DOWN_PREPARE_FROZEN:
+ num_cpus_frozen++;
+ partition_sched_domains(1, NULL, NULL);
+ break;
default:
return NOTIFY_DONE;
}
+ return NOTIFY_OK;
}

void __init sched_init_smp(void)
@@ -7589,6 +7658,7 @@ void sched_destroy_group(struct task_group *tg)
*/
void sched_move_task(struct task_struct *tsk)
{
+ struct task_group *tg;
int on_rq, running;
unsigned long flags;
struct rq *rq;
@@ -7603,6 +7673,12 @@ void sched_move_task(struct task_struct *tsk)
if (unlikely(running))
tsk->sched_class->put_prev_task(rq, tsk);

+ tg = container_of(task_subsys_state_check(tsk, cpu_cgroup_subsys_id,
+ lockdep_is_held(&tsk->sighand->siglock)),
+ struct task_group, css);
+ tg = autogroup_task_group(tsk, tg);
+ tsk->sched_task_group = tg;
+
#ifdef CONFIG_FAIR_GROUP_SCHED
if (tsk->sched_class->task_move_group)
tsk->sched_class->task_move_group(tsk, on_rq);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c099cc6..22321db 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2637,8 +2637,6 @@ static int select_idle_sibling(struct task_struct *p, int target)
int cpu = smp_processor_id();
int prev_cpu = task_cpu(p);
struct sched_domain *sd;
- struct sched_group *sg;
- int i;

/*
* If the task is going to be woken-up on this cpu and if it is
@@ -2655,29 +2653,17 @@ static int select_idle_sibling(struct task_struct *p, int target)
return prev_cpu;

/*
- * Otherwise, iterate the domains and find an elegible idle cpu.
+ * Otherwise, check assigned siblings to find an elegible idle cpu.
*/
sd = rcu_dereference(per_cpu(sd_llc, target));
- for_each_lower_domain(sd) {
- sg = sd->groups;
- do {
- if (!cpumask_intersects(sched_group_cpus(sg),
- tsk_cpus_allowed(p)))
- goto next;
-
- for_each_cpu(i, sched_group_cpus(sg)) {
- if (!idle_cpu(i))
- goto next;
- }

- target = cpumask_first_and(sched_group_cpus(sg),
- tsk_cpus_allowed(p));
- goto done;
-next:
- sg = sg->next;
- } while (sg != sd->groups);
+ for_each_lower_domain(sd) {
+ if (!cpumask_test_cpu(sd->idle_buddy, tsk_cpus_allowed(p)))
+ continue;
+ if (idle_cpu(sd->idle_buddy))
+ return sd->idle_buddy;
}
-done:
+
return target;
}

@@ -3068,16 +3054,19 @@ static unsigned long __read_mostly max_load_balance_interval = HZ/10;

#define LBF_ALL_PINNED 0x01
#define LBF_NEED_BREAK 0x02
+#define LBF_SOME_PINNED 0x04

struct lb_env {
struct sched_domain *sd;

- int src_cpu;
struct rq *src_rq;
+ int src_cpu;

int dst_cpu;
struct rq *dst_rq;

+ struct cpumask *dst_grpmask;
+ int new_dst_cpu;
enum cpu_idle_type idle;
long imbalance;
unsigned int flags;
@@ -3145,9 +3134,31 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
* 3) are cache-hot on their current CPU.
*/
if (!cpumask_test_cpu(env->dst_cpu, tsk_cpus_allowed(p))) {
+ int new_dst_cpu;
+
schedstat_inc(p, se.statistics.nr_failed_migrations_affine);
+
+ /*
+ * Remember if this task can be migrated to any other cpu in
+ * our sched_group. We may want to revisit it if we couldn't
+ * meet load balance goals by pulling other tasks on src_cpu.
+ *
+ * Also avoid computing new_dst_cpu if we have already computed
+ * one in current iteration.
+ */
+ if (!env->dst_grpmask || (env->flags & LBF_SOME_PINNED))
+ return 0;
+
+ new_dst_cpu = cpumask_first_and(env->dst_grpmask,
+ tsk_cpus_allowed(p));
+ if (new_dst_cpu < nr_cpu_ids) {
+ env->flags |= LBF_SOME_PINNED;
+ env->new_dst_cpu = new_dst_cpu;
+ }
return 0;
}
+
+ /* Record that we found atleast one task that could run on dst_cpu */
env->flags &= ~LBF_ALL_PINNED;

if (task_running(env->src_rq, p)) {
@@ -4227,7 +4238,8 @@ static int load_balance(int this_cpu, struct rq *this_rq,
struct sched_domain *sd, enum cpu_idle_type idle,
int *balance)
{
- int ld_moved, active_balance = 0;
+ int ld_moved, cur_ld_moved, active_balance = 0;
+ int lb_iterations, max_lb_iterations;
struct sched_group *group;
struct rq *busiest;
unsigned long flags;
@@ -4237,11 +4249,13 @@ static int load_balance(int this_cpu, struct rq *this_rq,
.sd = sd,
.dst_cpu = this_cpu,
.dst_rq = this_rq,
+ .dst_grpmask = sched_group_cpus(sd->groups),
.idle = idle,
.loop_break = sched_nr_migrate_break,
};

cpumask_copy(cpus, cpu_active_mask);
+ max_lb_iterations = cpumask_weight(env.dst_grpmask);

schedstat_inc(sd, lb_count[idle]);

@@ -4267,6 +4281,7 @@ redo:
schedstat_add(sd, lb_imbalance[idle], env.imbalance);

ld_moved = 0;
+ lb_iterations = 1;
if (busiest->nr_running > 1) {
/*
* Attempt to move tasks. If find_busiest_group has found
@@ -4284,7 +4299,13 @@ more_balance:
double_rq_lock(this_rq, busiest);
if (!env.loop)
update_h_load(env.src_cpu);
- ld_moved += move_tasks(&env);
+
+ /*
+ * cur_ld_moved - load moved in current iteration
+ * ld_moved - cumulative load moved across iterations
+ */
+ cur_ld_moved = move_tasks(&env);
+ ld_moved += cur_ld_moved;
double_rq_unlock(this_rq, busiest);
local_irq_restore(flags);

@@ -4296,14 +4317,52 @@ more_balance:
/*
* some other cpu did the load balance for us.
*/
- if (ld_moved && this_cpu != smp_processor_id())
- resched_cpu(this_cpu);
+ if (cur_ld_moved && env.dst_cpu != smp_processor_id())
+ resched_cpu(env.dst_cpu);
+
+ /*
+ * Revisit (affine) tasks on src_cpu that couldn't be moved to
+ * us and move them to an alternate dst_cpu in our sched_group
+ * where they can run. The upper limit on how many times we
+ * iterate on same src_cpu is dependent on number of cpus in our
+ * sched_group.
+ *
+ * This changes load balance semantics a bit on who can move
+ * load to a given_cpu. In addition to the given_cpu itself
+ * (or a ilb_cpu acting on its behalf where given_cpu is
+ * nohz-idle), we now have balance_cpu in a position to move
+ * load to given_cpu. In rare situations, this may cause
+ * conflicts (balance_cpu and given_cpu/ilb_cpu deciding
+ * _independently_ and at _same_ time to move some load to
+ * given_cpu) causing exceess load to be moved to given_cpu.
+ * This however should not happen so much in practice and
+ * moreover subsequent load balance cycles should correct the
+ * excess load moved.
+ */
+ if ((env.flags & LBF_SOME_PINNED) && env.imbalance > 0 &&
+ lb_iterations++ < max_lb_iterations) {
+
+ this_rq = cpu_rq(env.new_dst_cpu);
+ env.dst_rq = this_rq;
+ env.dst_cpu = env.new_dst_cpu;
+ env.flags &= ~LBF_SOME_PINNED;
+ env.loop = 0;
+ env.loop_break = sched_nr_migrate_break;
+ /*
+ * Go back to "more_balance" rather than "redo" since we
+ * need to continue with same src_cpu.
+ */
+ goto more_balance;
+ }

/* All tasks on this runqueue were pinned by CPU affinity */
if (unlikely(env.flags & LBF_ALL_PINNED)) {
cpumask_clear_cpu(cpu_of(busiest), cpus);
- if (!cpumask_empty(cpus))
+ if (!cpumask_empty(cpus)) {
+ env.loop = 0;
+ env.loop_break = sched_nr_migrate_break;
goto redo;
+ }
goto out_balanced;
}
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 55844f2..c35a1a7 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -538,22 +538,19 @@ extern int group_balance_cpu(struct sched_group *sg);
/*
* Return the group to which this tasks belongs.
*
- * We use task_subsys_state_check() and extend the RCU verification with
- * pi->lock and rq->lock because cpu_cgroup_attach() holds those locks for each
- * task it moves into the cgroup. Therefore by holding either of those locks,
- * we pin the task to the current cgroup.
+ * We cannot use task_subsys_state() and friends because the cgroup
+ * subsystem changes that value before the cgroup_subsys::attach() method
+ * is called, therefore we cannot pin it and might observe the wrong value.
+ *
+ * The same is true for autogroup's p->signal->autogroup->tg, the autogroup
+ * core changes this before calling sched_move_task().
+ *
+ * Instead we use a 'copy' which is updated from sched_move_task() while
+ * holding both task_struct::pi_lock and rq::lock.
*/
static inline struct task_group *task_group(struct task_struct *p)
{
- struct task_group *tg;
- struct cgroup_subsys_state *css;
-
- css = task_subsys_state_check(p, cpu_cgroup_subsys_id,
- lockdep_is_held(&p->pi_lock) ||
- lockdep_is_held(&task_rq(p)->lock));
- tg = container_of(css, struct task_group, css);
-
- return autogroup_task_group(p, tg);
+ return p->sched_task_group;
}

/* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */

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