ANNOUNCE: BLD-3.16 release.

From: Rakib Mullick
Date: Thu Aug 07 2014 - 14:02:33 EST

Hello everyone,

It's been quite a long time since the announcement of the Barbershop Load
Distribution (BLD) Algorithm. Quite a few changes have been made, since then.
Now it more reflects what it really should be ;-). It's a simplistic approach
towards load balancing, typical x86 SMP boxes should run okay (tested personally)
, but, yes it can break your boxes too. I'm looking forward to get some feedback,
to keep further development up and going.

(This patch is made for kernel version 3.16.)

Thanks,
Rakib
---

Signed-off-by: Rakib Mullick <rakib.mullick@xxxxxxxxx>

diff --git a/init/Kconfig b/init/Kconfig
index 9d76b99..847f34d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -36,6 +36,15 @@ config BROKEN_ON_SMP
depends on BROKEN || !SMP
default y

+config BLD
+ bool "An alternate CPU load distribution technique for task scheduler"
+ depends on SMP
+ default y
+ help
+ This is an alternate CPU load distribution technique based for task
+ scheduler based on The Barbershop Load Distribution algorithm. Not
+ suitable for NUMA, should work well on SMP.
+
config INIT_ENV_ARG_LIMIT
int
default 32 if !UML
diff --git a/kernel/sched/bld.h b/kernel/sched/bld.h
new file mode 100644
index 0000000..5a067c1
--- /dev/null
+++ b/kernel/sched/bld.h
@@ -0,0 +1,207 @@
+#ifdef CONFIG_BLD
+
+static DEFINE_RWLOCK(rt_list_lock);
+static LIST_HEAD(rt_rq_head);
+static LIST_HEAD(cfs_rq_head);
+static DEFINE_RWLOCK(cfs_list_lock);
+
+#ifdef CONFIG_FAIR_GROUP_SCHED
+static inline struct rq *rq_of_cfs(struct cfs_rq *cfs_rq)
+{
+ return cfs_rq->rq;
+}
+#else
+static inline struct rq *rq_of_cfs(struct cfs_rq *cfs_rq)
+{
+ return container_of(cfs_rq, struct rq, cfs);
+}
+#endif
+
+#ifdef CONFIG_RT_GROUP_SCHED
+static inline struct rq *rq_of_rt(struct rt_rq *rt_rq)
+{
+ return rt_rq->rq;
+}
+#else
+static inline struct rq *rq_of_rt(struct rt_rq *rt_rq)
+{
+ return container_of(rt_rq, struct rq, rt);
+}
+#endif
+
+static int select_cpu_for_wakeup(int task_type, struct cpumask *mask)
+{
+ int cpu = smp_processor_id(), i;
+ unsigned long load, min_load = ULONG_MAX;
+ struct rq *rq;
+
+ if (task_type) {
+ for_each_cpu(i, mask) {
+ rq = cpu_rq(i);
+ load = rq->cfs.load.weight;
+ if (load < min_load) {
+ min_load = load;
+ cpu = i;
+ }
+ }
+ } else {
+ min_load = -1;
+
+ for_each_cpu(i, mask) {
+ rq = cpu_rq(i);
+ load = rq->rt.lowbit;
+ if (load > min_load) {
+ min_load = load;
+ cpu = i;
+ }
+ }
+ }
+
+ return cpu;
+}
+
+static int bld_pick_cpu_cfs(struct task_struct *p, int sd_flags, int wake_flags)
+{
+ struct cfs_rq *cfs;
+ unsigned long flags;
+ unsigned int cpu = smp_processor_id();
+
+ read_lock_irqsave(&cfs_list_lock, flags);
+ list_for_each_entry(cfs, &cfs_rq_head, bld_cfs_list) {
+ cpu = cpu_of(rq_of_cfs(cfs));
+ if (cpu_online(cpu))
+ break;
+ }
+ read_unlock_irqrestore(&cfs_list_lock, flags);
+ return cpu;
+}
+
+static int bld_pick_cpu_rt(struct task_struct *p, int sd_flags, int wake_flags)
+{
+ struct rt_rq *rt;
+ unsigned long flags;
+ unsigned int cpu = smp_processor_id();
+
+ read_lock_irqsave(&rt_list_lock, flags);
+ list_for_each_entry(rt, &rt_rq_head, bld_rt_list) {
+ cpu = cpu_of(rq_of_rt(rt));
+ if (cpu_online(cpu))
+ break;
+ }
+ read_unlock_irqrestore(&rt_list_lock, flags);
+ return cpu;
+}
+
+static int bld_pick_cpu_domain(struct task_struct *p, int sd_flags, int wake_flags)
+{
+ unsigned int cpu = smp_processor_id(), want_affine = 0;
+ struct cpumask *tmpmask;
+
+ if (p->nr_cpus_allowed == 1)
+ return task_cpu(p);
+
+ if (sd_flags & SD_BALANCE_WAKE) {
+ if (cpumask_test_cpu(cpu, tsk_cpus_allowed(p))) {
+ want_affine = 1;
+ }
+ }
+
+ if (want_affine)
+ tmpmask = tsk_cpus_allowed(p);
+ else
+ tmpmask = sched_domain_span(cpu_rq(task_cpu(p))->sd);
+
+ if (rt_task(p))
+ cpu = select_cpu_for_wakeup(0, tmpmask);
+ else
+ cpu = select_cpu_for_wakeup(1, tmpmask);
+
+ return cpu;
+}
+
+static void track_load_rt(struct rq *rq, struct task_struct *p)
+{
+ unsigned long flag;
+ int firstbit;
+ struct rt_rq *first;
+ struct rt_prio_array *array = &rq->rt.active;
+
+ first = list_entry(rt_rq_head.next, struct rt_rq, bld_rt_list);
+ firstbit = sched_find_first_bit(array->bitmap);
+
+ /* Maintaining rt.lowbit */
+ if (firstbit <= rq->rt.lowbit)
+ rq->rt.lowbit = p->prio;
+
+ if (rq->rt.lowbit < first->lowbit) {
+ write_lock_irqsave(&rt_list_lock, flag);
+ list_del(&rq->rt.bld_rt_list);
+ list_add_tail(&rq->rt.bld_rt_list, &rt_rq_head);
+ write_unlock_irqrestore(&rt_list_lock, flag);
+ }
+}
+
+static int bld_get_cpu(struct task_struct *p, int sd_flags, int wake_flags)
+{
+ unsigned int cpu;
+
+ if (sd_flags == SD_BALANCE_WAKE || (sd_flags == SD_BALANCE_EXEC && (get_nr_threads(p) > 1)))
+ cpu = bld_pick_cpu_domain(p, sd_flags, wake_flags);
+ else {
+ if (rt_task(p))
+ cpu = bld_pick_cpu_rt(p, sd_flags, wake_flags);
+ else
+ cpu = bld_pick_cpu_cfs(p, sd_flags, wake_flags);
+ }
+
+ return cpu;
+}
+
+static void bld_track_load_activate(struct rq *rq, struct task_struct *p)
+{
+ unsigned long flag;
+ if (rt_task(p)) {
+ track_load_rt(rq, p);
+ } else {
+ if (rq->cfs.pos != 2) {
+ struct cfs_rq *last;
+ last = list_entry(cfs_rq_head.prev, struct cfs_rq, bld_cfs_list);
+ if (rq->cfs.load.weight >= last->load.weight) {
+ write_lock_irqsave(&cfs_list_lock, flag);
+ list_del(&rq->cfs.bld_cfs_list);
+ list_add_tail(&rq->cfs.bld_cfs_list, &cfs_rq_head);
+ rq->cfs.pos = 2; last->pos = 1;
+ write_unlock_irqrestore(&cfs_list_lock, flag);
+ }
+ }
+ }
+}
+
+static void bld_track_load_deactivate(struct rq *rq, struct task_struct *p)
+{
+ unsigned long flag;
+ if (rt_task(p)) {
+ track_load_rt(rq, p);
+ } else {
+ if (rq->cfs.pos != 0) {
+ struct cfs_rq *first;
+ first = list_entry(cfs_rq_head.next, struct cfs_rq, bld_cfs_list);
+ if (rq->cfs.load.weight <= first->load.weight) {
+ write_lock_irqsave(&cfs_list_lock, flag);
+ list_del(&rq->cfs.bld_cfs_list);
+ list_add(&rq->cfs.bld_cfs_list, &cfs_rq_head);
+ rq->cfs.pos = 0; first->pos = 1;
+ write_unlock_irqrestore(&cfs_list_lock, flag);
+ }
+ }
+ }
+}
+#else
+static inline void bld_track_load_activate(struct rq *rq)
+{
+}
+
+static inline void bld_track_load_deactivate(struct rq *rq)
+{
+}
+#endif /* CONFIG_BLD */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bc1638b..b429ce5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -24,6 +24,8 @@
* 2007-07-01 Group scheduling enhancements by Srivatsa Vaddagiri
* 2007-11-29 RT balancing improvements by Steven Rostedt, Gregory Haskins,
* Thomas Gleixner, Mike Kravetz
+ * 2012-Feb The Barbershop Load Distribution (BLD) algorithm - an alternate
+ * CPU load distribution technique for kernel scheduler by Rakib Mullick.
*/

#include <linux/mm.h>
@@ -86,6 +88,7 @@
#include "sched.h"
#include "../workqueue_internal.h"
#include "../smpboot.h"
+#include "bld.h"

#define CREATE_TRACE_POINTS
#include <trace/events/sched.h>
@@ -831,6 +834,8 @@ static void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
update_rq_clock(rq);
sched_info_queued(rq, p);
p->sched_class->enqueue_task(rq, p, flags);
+ if (!dl_task(p))
+ bld_track_load_activate(rq, p);
}

static void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
@@ -838,6 +843,8 @@ static void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
update_rq_clock(rq);
sched_info_dequeued(rq, p);
p->sched_class->dequeue_task(rq, p, flags);
+ if (!dl_task(p))
+ bld_track_load_deactivate(rq, p);
}

void activate_task(struct rq *rq, struct task_struct *p, int flags)
@@ -1398,7 +1405,14 @@ out:
static inline
int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags)
{
+#ifndef CONFIG_BLD
cpu = p->sched_class->select_task_rq(p, cpu, sd_flags, wake_flags);
+#else
+ if (dl_task(p))
+ cpu = dl_sched_class.select_task_rq(p, cpu, sd_flags, wake_flags);
+ else
+ cpu = bld_get_cpu(p, sd_flags, wake_flags);
+#endif

/*
* In order not to call set_task_cpu() on a blocking task we need
@@ -1568,9 +1582,13 @@ void scheduler_ipi(void)
*/
preempt_fold_need_resched();

+#ifndef CONFIG_BLD
if (llist_empty(&this_rq()->wake_list)
&& !tick_nohz_full_cpu(smp_processor_id())
&& !got_nohz_idle_kick())
+#else
+ if (llist_empty(&this_rq()->wake_list) && !tick_nohz_full_cpu(smp_processor_id()))
+#endif
return;

/*
@@ -1593,13 +1611,16 @@ void scheduler_ipi(void)
/*
* Check if someone kicked us for doing the nohz idle load balance.
*/
+#ifndef CONFIG_BLD
if (unlikely(got_nohz_idle_kick())) {
this_rq()->idle_balance = 1;
raise_softirq_irqoff(SCHED_SOFTIRQ);
}
+#endif
irq_exit();
}

+#ifndef CONFIG_BLD
static void ttwu_queue_remote(struct task_struct *p, int cpu)
{
struct rq *rq = cpu_rq(cpu);
@@ -1611,6 +1632,7 @@ static void ttwu_queue_remote(struct task_struct *p, int cpu)
trace_sched_wake_idle_without_ipi(cpu);
}
}
+#endif

bool cpus_share_cache(int this_cpu, int that_cpu)
{
@@ -1622,7 +1644,7 @@ static void ttwu_queue(struct task_struct *p, int cpu)
{
struct rq *rq = cpu_rq(cpu);

-#if defined(CONFIG_SMP)
+#if defined(CONFIG_SMP) && !defined(CONFIG_BLD)
if (sched_feat(TTWU_QUEUE) && !cpus_share_cache(smp_processor_id(), cpu)) {
sched_clock_cpu(cpu); /* sync clocks x-cpu */
ttwu_queue_remote(p, cpu);
@@ -1930,7 +1952,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
* Silence PROVE_RCU.
*/
raw_spin_lock_irqsave(&p->pi_lock, flags);
- set_task_cpu(p, cpu);
+ __set_task_cpu(p, cpu);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);

#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
@@ -2398,7 +2420,14 @@ void sched_exec(void)
int dest_cpu;

raw_spin_lock_irqsave(&p->pi_lock, flags);
+#ifndef CONFIG_BLD
dest_cpu = p->sched_class->select_task_rq(p, task_cpu(p), SD_BALANCE_EXEC, 0);
+#else
+ if (dl_task(p))
+ dest_cpu = task_cpu(p);
+ else
+ dest_cpu = bld_get_cpu(p, SD_BALANCE_EXEC, 0);
+#endif
if (dest_cpu == smp_processor_id())
goto unlock;

@@ -2508,8 +2537,10 @@ void scheduler_tick(void)

#ifdef CONFIG_SMP
rq->idle_balance = idle_cpu(cpu);
+#ifndef CONFIG_BLD
trigger_load_balance(rq);
#endif
+#endif
rq_last_tick_reset(rq);
}

@@ -6990,6 +7021,15 @@ void __init sched_init(void)
#endif
init_rq_hrtick(rq);
atomic_set(&rq->nr_iowait, 0);
+#ifdef CONFIG_BLD
+ INIT_LIST_HEAD(&rq->cfs.bld_cfs_list);
+ list_add_tail(&rq->cfs.bld_cfs_list, &cfs_rq_head);
+ rq->cfs.pos = 0;
+
+ INIT_LIST_HEAD(&rq->rt.bld_rt_list);
+ list_add_tail(&rq->rt.bld_rt_list, &rt_rq_head);
+ rq->rt.lowbit = INT_MAX;
+#endif
}

set_load_weight(&init_task);
@@ -7030,6 +7070,9 @@ void __init sched_init(void)
init_sched_fair_class();

scheduler_running = 1;
+#ifdef CONFIG_BLD
+ printk(KERN_INFO "BLD: An Alternate CPU load distributor activated.\n");
+#endif
}

#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fea7d33..651aa1d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4101,6 +4101,7 @@ static void task_waking_fair(struct task_struct *p)
record_wakee(p);
}

+#ifndef CONFIG_BLD
#ifdef CONFIG_FAIR_GROUP_SCHED
/*
* effective_load() calculates the load change as seen from the root_task_group
@@ -4550,6 +4551,7 @@ unlock:

return new_cpu;
}
+#endif /* CONFIG_BLD */

/*
* Called immediately before a task is migrated to a new cpu; task_cpu(p) and
@@ -4845,6 +4847,7 @@ simple:
return p;

idle:
+#ifndef CONFIG_BLD
new_tasks = idle_balance(rq);
/*
* Because idle_balance() releases (and re-acquires) rq->lock, it is
@@ -4856,7 +4859,7 @@ idle:

if (new_tasks > 0)
goto again;
-
+#endif
return NULL;
}

@@ -6931,12 +6934,40 @@ static inline int on_null_domain(struct rq *rq)
* needed, they will kick the idle load balancer, which then does idle
* load balancing for all the idle CPUs.
*/
+#ifndef CONFIG_BLD
static struct {
cpumask_var_t idle_cpus_mask;
atomic_t nr_cpus;
unsigned long next_balance; /* in jiffy units */
} nohz ____cacheline_aligned;

+static inline void nohz_balance_exit_idle(int cpu)
+{
+ if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
+ /*
+ * Completely isolated CPUs don't ever set, so we must test.
+ */
+ if (likely(cpumask_test_cpu(cpu, nohz.idle_cpus_mask))) {
+ cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
+ atomic_dec(&nohz.nr_cpus);
+ }
+ clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
+ }
+}
+
+static int sched_ilb_notifier(struct notifier_block *nfb,
+ unsigned long action, void *hcpu)
+{
+ switch (action & ~CPU_TASKS_FROZEN) {
+ case CPU_DYING:
+ nohz_balance_exit_idle(smp_processor_id());
+ return NOTIFY_OK;
+ default:
+ return NOTIFY_DONE;
+ }
+}
+#endif /* CONFIG_BLD */
+
static inline int find_new_ilb(void)
{
int ilb = cpumask_first(nohz.idle_cpus_mask);
@@ -6975,20 +7006,6 @@ static void nohz_balancer_kick(void)
return;
}

-static inline void nohz_balance_exit_idle(int cpu)
-{
- if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
- /*
- * Completely isolated CPUs don't ever set, so we must test.
- */
- if (likely(cpumask_test_cpu(cpu, nohz.idle_cpus_mask))) {
- cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
- atomic_dec(&nohz.nr_cpus);
- }
- clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
- }
-}
-
static inline void set_cpu_sd_state_busy(void)
{
struct sched_domain *sd;
@@ -7029,6 +7046,7 @@ unlock:
*/
void nohz_balance_enter_idle(int cpu)
{
+#ifndef CONFIG_BLD
/*
* If this cpu is going down, then nothing needs to be done.
*/
@@ -7047,23 +7065,10 @@ void nohz_balance_enter_idle(int cpu)
cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
atomic_inc(&nohz.nr_cpus);
set_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
-}
-
-static int sched_ilb_notifier(struct notifier_block *nfb,
- unsigned long action, void *hcpu)
-{
- switch (action & ~CPU_TASKS_FROZEN) {
- case CPU_DYING:
- nohz_balance_exit_idle(smp_processor_id());
- return NOTIFY_OK;
- default:
- return NOTIFY_DONE;
- }
+#endif
}
#endif

-static DEFINE_SPINLOCK(balancing);
-
/*
* Scale the max load_balance interval with the number of CPUs in the system.
* This trades load-balance latency on larger machines for less cross talk.
@@ -7073,6 +7078,9 @@ void update_max_interval(void)
max_load_balance_interval = HZ*num_online_cpus()/10;
}

+#ifndef CONFIG_BLD
+static DEFINE_SPINLOCK(balancing);
+
/*
* It checks each scheduling domain to see if it is due to be balanced,
* and initiates a balancing operation if so.
@@ -7321,6 +7329,7 @@ void trigger_load_balance(struct rq *rq)
nohz_balancer_kick();
#endif
}
+#endif /* CONFIG_BLD */

static void rq_online_fair(struct rq *rq)
{
@@ -7764,7 +7773,9 @@ const struct sched_class fair_sched_class = {
.put_prev_task = put_prev_task_fair,

#ifdef CONFIG_SMP
+#ifndef CONFIG_BLD
.select_task_rq = select_task_rq_fair,
+#endif
.migrate_task_rq = migrate_task_rq_fair,

.rq_online = rq_online_fair,
@@ -7802,6 +7813,7 @@ void print_cfs_stats(struct seq_file *m, int cpu)

__init void init_sched_fair_class(void)
{
+#ifndef CONFIG_BLD
#ifdef CONFIG_SMP
open_softirq(SCHED_SOFTIRQ, run_rebalance_domains);

@@ -7811,5 +7823,5 @@ __init void init_sched_fair_class(void)
cpu_notifier(sched_ilb_notifier, 0);
#endif
#endif /* SMP */
-
+#endif /* BLD */
}
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index a490831..c9d22c3 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1291,6 +1291,7 @@ static void yield_task_rt(struct rq *rq)
#ifdef CONFIG_SMP
static int find_lowest_rq(struct task_struct *task);

+#ifndef CONFIG_BLD
static int
select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags)
{
@@ -1344,6 +1345,7 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags)
out:
return cpu;
}
+#endif /* CONFIG_BLD */

static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
{
@@ -2108,7 +2110,9 @@ const struct sched_class rt_sched_class = {
.put_prev_task = put_prev_task_rt,

#ifdef CONFIG_SMP
+#ifndef CONFIG_BLD
.select_task_rq = select_task_rq_rt,
+#endif

.set_cpus_allowed = set_cpus_allowed_rt,
.rq_online = rq_online_rt,
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 31cc02e..1c497d2 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -358,9 +358,8 @@ struct cfs_rq {
#endif /* CONFIG_FAIR_GROUP_SCHED */
#endif /* CONFIG_SMP */

-#ifdef CONFIG_FAIR_GROUP_SCHED
struct rq *rq; /* cpu runqueue to which this cfs_rq is attached */
-
+#ifdef CONFIG_FAIR_GROUP_SCHED
/*
* leaf cfs_rqs are those that hold tasks (lowest schedulable entity in
* a hierarchy). Non-leaf lrqs hold other higher schedulable entities
@@ -384,6 +383,11 @@ struct cfs_rq {
struct list_head throttled_list;
#endif /* CONFIG_CFS_BANDWIDTH */
#endif /* CONFIG_FAIR_GROUP_SCHED */
+
+#ifdef CONFIG_BLD
+ struct list_head bld_cfs_list;
+ char pos;
+#endif
};

static inline int rt_bandwidth_enabled(void)
@@ -417,12 +421,16 @@ struct rt_rq {
/* Nests inside the rq lock: */
raw_spinlock_t rt_runtime_lock;

+ struct rq *rq;
#ifdef CONFIG_RT_GROUP_SCHED
unsigned long rt_nr_boosted;

- struct rq *rq;
struct task_group *tg;
#endif
+#ifdef CONFIG_BLD
+ struct list_head bld_rt_list;
+ int lowbit;
+#endif
};

/* Deadline class' related fields in a runqueue */



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