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sched: revert load_balance_monitor() changes 

The following commits cause a number of regressions:

  commit 58e2d4ca58
  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
  Date:   Fri Jan 25 21:08:00 2008 +0100
  sched: group scheduling, change how cpu load is calculated

  commit 6b2d770026
  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
  Date:   Fri Jan 25 21:08:00 2008 +0100
  sched: group scheduler, fix fairness of cpu bandwidth allocation for task groups

Namely:
 - very frequent wakeups on SMP, reported by PowerTop users.
 - cacheline trashing on (large) SMP
 - some latencies larger than 500ms

While there is a mergeable patch to fix the latter, the former issues
are not fixable in a manner suitable for .25 (we're at -rc3 now).

Hence we revert them and try again in v2.6.26.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Tested-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2008-02-25 17:34:02 +01:00 committed by Ingo Molnar
parent 976dde010e
commit 62fb185130
5 changed files with 71 additions and 355 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/linux/sched.h
View File

@ -1542,10 +1542,6 @@ extern unsigned int sysctl_sched_child_runs_first;
extern unsigned int sysctl_sched_features;
extern unsigned int sysctl_sched_migration_cost;
extern unsigned int sysctl_sched_nr_migrate;
#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP)
extern unsigned int sysctl_sched_min_bal_int_shares;
extern unsigned int sysctl_sched_max_bal_int_shares;
#endif
int sched_nr_latency_handler(struct ctl_table *table, int write,
struct file *file, void __user *buffer, size_t *length,

285
kernel/sched.c
View File

@ -174,41 +174,6 @@ struct task_group {
struct sched_entity **se;
/* runqueue "owned" by this group on each cpu */
struct cfs_rq **cfs_rq;
/*
* shares assigned to a task group governs how much of cpu bandwidth
* is allocated to the group. The more shares a group has, the more is
* the cpu bandwidth allocated to it.
*
* For ex, lets say that there are three task groups, A, B and C which
* have been assigned shares 1000, 2000 and 3000 respectively. Then,
* cpu bandwidth allocated by the scheduler to task groups A, B and C
* should be:
*
* Bw(A) = 1000/(1000+2000+3000) * 100 = 16.66%
* Bw(B) = 2000/(1000+2000+3000) * 100 = 33.33%
* Bw(C) = 3000/(1000+2000+3000) * 100 = 50%
*
* The weight assigned to a task group's schedulable entities on every
* cpu (task_group.se[a_cpu]->load.weight) is derived from the task
* group's shares. For ex: lets say that task group A has been
* assigned shares of 1000 and there are two CPUs in a system. Then,
*
* tg_A->se[0]->load.weight = tg_A->se[1]->load.weight = 1000;
*
* Note: It's not necessary that each of a task's group schedulable
* entity have the same weight on all CPUs. If the group
* has 2 of its tasks on CPU0 and 1 task on CPU1, then a
* better distribution of weight could be:
*
* tg_A->se[0]->load.weight = 2/3 * 2000 = 1333
* tg_A->se[1]->load.weight = 1/2 * 2000 = 667
*
* rebalance_shares() is responsible for distributing the shares of a
* task groups like this among the group's schedulable entities across
* cpus.
*
*/
unsigned long shares;
#endif
@ -250,22 +215,12 @@ static DEFINE_SPINLOCK(task_group_lock);
static DEFINE_MUTEX(doms_cur_mutex);
#ifdef CONFIG_FAIR_GROUP_SCHED
#ifdef CONFIG_SMP
/* kernel thread that runs rebalance_shares() periodically */
static struct task_struct *lb_monitor_task;
static int load_balance_monitor(void *unused);
#endif
static void set_se_shares(struct sched_entity *se, unsigned long shares);
#ifdef CONFIG_USER_SCHED
# define INIT_TASK_GROUP_LOAD (2*NICE_0_LOAD)
#else
# define INIT_TASK_GROUP_LOAD NICE_0_LOAD
#endif
#define MIN_GROUP_SHARES 2
static int init_task_group_load = INIT_TASK_GROUP_LOAD;
#endif
@ -1245,16 +1200,6 @@ static void cpuacct_charge(struct task_struct *tsk, u64 cputime);
static inline void cpuacct_charge(struct task_struct *tsk, u64 cputime) {}
#endif
static inline void inc_cpu_load(struct rq *rq, unsigned long load)
{
update_load_add(&rq->load, load);
}
static inline void dec_cpu_load(struct rq *rq, unsigned long load)
{
update_load_sub(&rq->load, load);
}
#ifdef CONFIG_SMP
static unsigned long source_load(int cpu, int type);
static unsigned long target_load(int cpu, int type);
@ -1272,14 +1217,26 @@ static int task_hot(struct task_struct *p, u64 now, struct sched_domain *sd);
#define sched_class_highest (&rt_sched_class)
static void inc_nr_running(struct rq *rq)
static inline void inc_load(struct rq *rq, const struct task_struct *p)
{
rq->nr_running++;
update_load_add(&rq->load, p->se.load.weight);
}
static void dec_nr_running(struct rq *rq)
static inline void dec_load(struct rq *rq, const struct task_struct *p)
{
update_load_sub(&rq->load, p->se.load.weight);
}
static void inc_nr_running(struct task_struct *p, struct rq *rq)
{
rq->nr_running++;
inc_load(rq, p);
}
static void dec_nr_running(struct task_struct *p, struct rq *rq)
{
rq->nr_running--;
dec_load(rq, p);
}
static void set_load_weight(struct task_struct *p)
@ -1371,7 +1328,7 @@ static void activate_task(struct rq *rq, struct task_struct *p, int wakeup)
rq->nr_uninterruptible--;
enqueue_task(rq, p, wakeup);
inc_nr_running(rq);
inc_nr_running(p, rq);
}
/*
@ -1383,7 +1340,7 @@ static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep)
rq->nr_uninterruptible++;
dequeue_task(rq, p, sleep);
dec_nr_running(rq);
dec_nr_running(p, rq);
}
/**
@ -2023,7 +1980,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
* management (if any):
*/
p->sched_class->task_new(rq, p);
inc_nr_running(rq);
inc_nr_running(p, rq);
}
check_preempt_curr(rq, p);
#ifdef CONFIG_SMP
@ -4362,8 +4319,10 @@ void set_user_nice(struct task_struct *p, long nice)
goto out_unlock;
}
on_rq = p->se.on_rq;
if (on_rq)
if (on_rq) {
dequeue_task(rq, p, 0);
dec_load(rq, p);
}
p->static_prio = NICE_TO_PRIO(nice);
set_load_weight(p);
@ -4373,6 +4332,7 @@ void set_user_nice(struct task_struct *p, long nice)
if (on_rq) {
enqueue_task(rq, p, 0);
inc_load(rq, p);
/*
* If the task increased its priority or is running and
* lowered its priority, then reschedule its CPU:
@ -7087,21 +7047,6 @@ void __init sched_init_smp(void)
if (set_cpus_allowed(current, non_isolated_cpus) < 0)
BUG();
sched_init_granularity();
#ifdef CONFIG_FAIR_GROUP_SCHED
if (nr_cpu_ids == 1)
return;
lb_monitor_task = kthread_create(load_balance_monitor, NULL,
"group_balance");
if (!IS_ERR(lb_monitor_task)) {
lb_monitor_task->flags |= PF_NOFREEZE;
wake_up_process(lb_monitor_task);
} else {
printk(KERN_ERR "Could not create load balance monitor thread"
"(error = %ld) \n", PTR_ERR(lb_monitor_task));
}
#endif
}
#else
void __init sched_init_smp(void)
@ -7424,157 +7369,6 @@ void set_curr_task(int cpu, struct task_struct *p)
#ifdef CONFIG_GROUP_SCHED
#if defined CONFIG_FAIR_GROUP_SCHED && defined CONFIG_SMP
/*
* distribute shares of all task groups among their schedulable entities,
* to reflect load distribution across cpus.
*/
static int rebalance_shares(struct sched_domain *sd, int this_cpu)
{
struct cfs_rq *cfs_rq;
struct rq *rq = cpu_rq(this_cpu);
cpumask_t sdspan = sd->span;
int balanced = 1;
/* Walk thr' all the task groups that we have */
for_each_leaf_cfs_rq(rq, cfs_rq) {
int i;
unsigned long total_load = 0, total_shares;
struct task_group *tg = cfs_rq->tg;
/* Gather total task load of this group across cpus */
for_each_cpu_mask(i, sdspan)
total_load += tg->cfs_rq[i]->load.weight;
/* Nothing to do if this group has no load */
if (!total_load)
continue;
/*
* tg->shares represents the number of cpu shares the task group
* is eligible to hold on a single cpu. On N cpus, it is
* eligible to hold (N * tg->shares) number of cpu shares.
*/
total_shares = tg->shares * cpus_weight(sdspan);
/*
* redistribute total_shares across cpus as per the task load
* distribution.
*/
for_each_cpu_mask(i, sdspan) {
unsigned long local_load, local_shares;
local_load = tg->cfs_rq[i]->load.weight;
local_shares = (local_load * total_shares) / total_load;
if (!local_shares)
local_shares = MIN_GROUP_SHARES;
if (local_shares == tg->se[i]->load.weight)
continue;
spin_lock_irq(&cpu_rq(i)->lock);
set_se_shares(tg->se[i], local_shares);
spin_unlock_irq(&cpu_rq(i)->lock);
balanced = 0;
}
}
return balanced;
}
/*
* How frequently should we rebalance_shares() across cpus?
*
* The more frequently we rebalance shares, the more accurate is the fairness
* of cpu bandwidth distribution between task groups. However higher frequency
* also implies increased scheduling overhead.
*
* sysctl_sched_min_bal_int_shares represents the minimum interval between
* consecutive calls to rebalance_shares() in the same sched domain.
*
* sysctl_sched_max_bal_int_shares represents the maximum interval between
* consecutive calls to rebalance_shares() in the same sched domain.
*
* These settings allows for the appropriate trade-off between accuracy of
* fairness and the associated overhead.
*
*/
/* default: 8ms, units: milliseconds */
const_debug unsigned int sysctl_sched_min_bal_int_shares = 8;
/* default: 128ms, units: milliseconds */
const_debug unsigned int sysctl_sched_max_bal_int_shares = 128;
/* kernel thread that runs rebalance_shares() periodically */
static int load_balance_monitor(void *unused)
{
unsigned int timeout = sysctl_sched_min_bal_int_shares;
struct sched_param schedparm;
int ret;
/*
* We don't want this thread's execution to be limited by the shares
* assigned to default group (init_task_group). Hence make it run
* as a SCHED_RR RT task at the lowest priority.
*/
schedparm.sched_priority = 1;
ret = sched_setscheduler(current, SCHED_RR, &schedparm);
if (ret)
printk(KERN_ERR "Couldn't set SCHED_RR policy for load balance"
" monitor thread (error = %d) \n", ret);
while (!kthread_should_stop()) {
int i, cpu, balanced = 1;
/* Prevent cpus going down or coming up */
get_online_cpus();
/* lockout changes to doms_cur[] array */
lock_doms_cur();
/*
* Enter a rcu read-side critical section to safely walk rq->sd
* chain on various cpus and to walk task group list
* (rq->leaf_cfs_rq_list) in rebalance_shares().
*/
rcu_read_lock();
for (i = 0; i < ndoms_cur; i++) {
cpumask_t cpumap = doms_cur[i];
struct sched_domain *sd = NULL, *sd_prev = NULL;
cpu = first_cpu(cpumap);
/* Find the highest domain at which to balance shares */
for_each_domain(cpu, sd) {
if (!(sd->flags & SD_LOAD_BALANCE))
continue;
sd_prev = sd;
}
sd = sd_prev;
/* sd == NULL? No load balance reqd in this domain */
if (!sd)
continue;
balanced &= rebalance_shares(sd, cpu);
}
rcu_read_unlock();
unlock_doms_cur();
put_online_cpus();
if (!balanced)
timeout = sysctl_sched_min_bal_int_shares;
else if (timeout < sysctl_sched_max_bal_int_shares)
timeout *= 2;
msleep_interruptible(timeout);
}
return 0;
}
#endif /* CONFIG_SMP */
#ifdef CONFIG_FAIR_GROUP_SCHED
static void free_fair_sched_group(struct task_group *tg)
{
@ -7841,29 +7635,25 @@ void sched_move_task(struct task_struct *tsk)
}
#ifdef CONFIG_FAIR_GROUP_SCHED
/* rq->lock to be locked by caller */
static void set_se_shares(struct sched_entity *se, unsigned long shares)
{
struct cfs_rq *cfs_rq = se->cfs_rq;
struct rq *rq = cfs_rq->rq;
int on_rq;
if (!shares)
shares = MIN_GROUP_SHARES;
spin_lock_irq(&rq->lock);
on_rq = se->on_rq;
if (on_rq) {
if (on_rq)
dequeue_entity(cfs_rq, se, 0);
dec_cpu_load(rq, se->load.weight);
}
se->load.weight = shares;
se->load.inv_weight = div64_64((1ULL<<32), shares);
if (on_rq) {
if (on_rq)
enqueue_entity(cfs_rq, se, 0);
inc_cpu_load(rq, se->load.weight);
}
spin_unlock_irq(&rq->lock);
}
static DEFINE_MUTEX(shares_mutex);
@ -7873,18 +7663,18 @@ int sched_group_set_shares(struct task_group *tg, unsigned long shares)
int i;
unsigned long flags;
/*
* A weight of 0 or 1 can cause arithmetics problems.
* (The default weight is 1024 - so there's no practical
* limitation from this.)
*/
if (shares < 2)
shares = 2;
mutex_lock(&shares_mutex);
if (tg->shares == shares)
goto done;
if (shares < MIN_GROUP_SHARES)
shares = MIN_GROUP_SHARES;
/*
* Prevent any load balance activity (rebalance_shares,
* load_balance_fair) from referring to this group first,
* by taking it off the rq->leaf_cfs_rq_list on each cpu.
*/
spin_lock_irqsave(&task_group_lock, flags);
for_each_possible_cpu(i)
unregister_fair_sched_group(tg, i);
@ -7898,11 +7688,8 @@ int sched_group_set_shares(struct task_group *tg, unsigned long shares)
* w/o tripping rebalance_share or load_balance_fair.
*/
tg->shares = shares;
for_each_possible_cpu(i) {
spin_lock_irq(&cpu_rq(i)->lock);
for_each_possible_cpu(i)
set_se_shares(tg->se[i], shares);
spin_unlock_irq(&cpu_rq(i)->lock);
}
/*
* Enable load balance activity on this group, by inserting it back on

115
kernel/sched_fair.c
View File

@ -727,8 +727,6 @@ static inline struct sched_entity *parent_entity(struct sched_entity *se)
return se->parent;
}
#define GROUP_IMBALANCE_PCT 20
#else /* CONFIG_FAIR_GROUP_SCHED */
#define for_each_sched_entity(se) \
@ -819,26 +817,15 @@ hrtick_start_fair(struct rq *rq, struct task_struct *p)
static void enqueue_task_fair(struct rq *rq, struct task_struct *p, int wakeup)
{
struct cfs_rq *cfs_rq;
struct sched_entity *se = &p->se,
*topse = NULL; /* Highest schedulable entity */
int incload = 1;
struct sched_entity *se = &p->se;
for_each_sched_entity(se) {
topse = se;
if (se->on_rq) {
incload = 0;
if (se->on_rq)
break;
}
cfs_rq = cfs_rq_of(se);
enqueue_entity(cfs_rq, se, wakeup);
wakeup = 1;
}
/* Increment cpu load if we just enqueued the first task of a group on
* 'rq->cpu'. 'topse' represents the group to which task 'p' belongs
* at the highest grouping level.
*/
if (incload)
inc_cpu_load(rq, topse->load.weight);
hrtick_start_fair(rq, rq->curr);
}
@ -851,28 +838,16 @@ static void enqueue_task_fair(struct rq *rq, struct task_struct *p, int wakeup)
static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int sleep)
{
struct cfs_rq *cfs_rq;
struct sched_entity *se = &p->se,
*topse = NULL; /* Highest schedulable entity */
int decload = 1;
struct sched_entity *se = &p->se;
for_each_sched_entity(se) {
topse = se;
cfs_rq = cfs_rq_of(se);
dequeue_entity(cfs_rq, se, sleep);
/* Don't dequeue parent if it has other entities besides us */
if (cfs_rq->load.weight) {
if (parent_entity(se))
decload = 0;
if (cfs_rq->load.weight)
break;
}
sleep = 1;
}
/* Decrement cpu load if we just dequeued the last task of a group on
* 'rq->cpu'. 'topse' represents the group to which task 'p' belongs
* at the highest grouping level.
*/
if (decload)
dec_cpu_load(rq, topse->load.weight);
hrtick_start_fair(rq, rq->curr);
}
@ -1186,6 +1161,25 @@ static struct task_struct *load_balance_next_fair(void *arg)
return __load_balance_iterator(cfs_rq, cfs_rq->rb_load_balance_curr);
}
#ifdef CONFIG_FAIR_GROUP_SCHED
static int cfs_rq_best_prio(struct cfs_rq *cfs_rq)
{
struct sched_entity *curr;
struct task_struct *p;
if (!cfs_rq->nr_running || !first_fair(cfs_rq))
return MAX_PRIO;
curr = cfs_rq->curr;
if (!curr)
curr = __pick_next_entity(cfs_rq);
p = task_of(curr);
return p->prio;
}
#endif
static unsigned long
load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
unsigned long max_load_move,
@ -1195,45 +1189,28 @@ load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
struct cfs_rq *busy_cfs_rq;
long rem_load_move = max_load_move;
struct rq_iterator cfs_rq_iterator;
unsigned long load_moved;
cfs_rq_iterator.start = load_balance_start_fair;
cfs_rq_iterator.next = load_balance_next_fair;
for_each_leaf_cfs_rq(busiest, busy_cfs_rq) {
#ifdef CONFIG_FAIR_GROUP_SCHED
struct cfs_rq *this_cfs_rq = busy_cfs_rq->tg->cfs_rq[this_cpu];
unsigned long maxload, task_load, group_weight;
unsigned long thisload, per_task_load;
struct sched_entity *se = busy_cfs_rq->tg->se[busiest->cpu];
struct cfs_rq *this_cfs_rq;
long imbalance;
unsigned long maxload;
task_load = busy_cfs_rq->load.weight;
group_weight = se->load.weight;
this_cfs_rq = cpu_cfs_rq(busy_cfs_rq, this_cpu);
/*
* 'group_weight' is contributed by tasks of total weight
* 'task_load'. To move 'rem_load_move' worth of weight only,
* we need to move a maximum task load of:
*
* maxload = (remload / group_weight) * task_load;
*/
maxload = (rem_load_move * task_load) / group_weight;
if (!maxload || !task_load)
imbalance = busy_cfs_rq->load.weight - this_cfs_rq->load.weight;
/* Don't pull if this_cfs_rq has more load than busy_cfs_rq */
if (imbalance <= 0)
continue;
per_task_load = task_load / busy_cfs_rq->nr_running;
/*
* balance_tasks will try to forcibly move atleast one task if
* possible (because of SCHED_LOAD_SCALE_FUZZ). Avoid that if
* maxload is less than GROUP_IMBALANCE_FUZZ% the per_task_load.
*/
if (100 * maxload < GROUP_IMBALANCE_PCT * per_task_load)
continue;
/* Don't pull more than imbalance/2 */
imbalance /= 2;
maxload = min(rem_load_move, imbalance);
/* Disable priority-based load balance */
*this_best_prio = 0;
thisload = this_cfs_rq->load.weight;
*this_best_prio = cfs_rq_best_prio(this_cfs_rq);
#else
# define maxload rem_load_move
#endif
@ -1242,33 +1219,11 @@ load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
* load_balance_[start|next]_fair iterators
*/
cfs_rq_iterator.arg = busy_cfs_rq;
load_moved = balance_tasks(this_rq, this_cpu, busiest,
rem_load_move -= balance_tasks(this_rq, this_cpu, busiest,
maxload, sd, idle, all_pinned,
this_best_prio,
&cfs_rq_iterator);
#ifdef CONFIG_FAIR_GROUP_SCHED
/*
* load_moved holds the task load that was moved. The
* effective (group) weight moved would be:
* load_moved_eff = load_moved/task_load * group_weight;
*/
load_moved = (group_weight * load_moved) / task_load;
/* Adjust shares on both cpus to reflect load_moved */
group_weight -= load_moved;
set_se_shares(se, group_weight);
se = busy_cfs_rq->tg->se[this_cpu];
if (!thisload)
group_weight = load_moved;
else
group_weight = se->load.weight + load_moved;
set_se_shares(se, group_weight);
#endif
rem_load_move -= load_moved;
if (rem_load_move <= 0)
break;
}

4
kernel/sched_rt.c
View File

@ -393,8 +393,6 @@ static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
*/
for_each_sched_rt_entity(rt_se)
enqueue_rt_entity(rt_se);
inc_cpu_load(rq, p->se.load.weight);
}
static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
@ -414,8 +412,6 @@ static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
if (rt_rq && rt_rq->rt_nr_running)
enqueue_rt_entity(rt_se);
}
dec_cpu_load(rq, p->se.load.weight);
}
/*

18
kernel/sysctl.c
View File

@ -311,24 +311,6 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP)
{
.ctl_name = CTL_UNNUMBERED,
.procname = "sched_min_bal_int_shares",
.data = &sysctl_sched_min_bal_int_shares,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = &proc_dointvec,
},
{
.ctl_name = CTL_UNNUMBERED,
.procname = "sched_max_bal_int_shares",
.data = &sysctl_sched_max_bal_int_shares,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = &proc_dointvec,
},
#endif
#endif
{
.ctl_name = CTL_UNNUMBERED,