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Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Browse source 
Pull scheduler changes from Ingo Molnar:
 "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."

* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched: Fix race in task_group()
  sched: Improve balance_cpu() to consider other cpus in its group as target of (pinned) task
  sched: Reset loop counters if all tasks are pinned and we need to redo load balance
  sched: Reorder 'struct lb_env' members to reduce its size
  sched: Improve scalability via 'CPU buddies', which withstand random perturbations
  cpusets: Remove/update outdated comments
  cpusets, hotplug: Restructure functions that are invoked during hotplug
  cpusets, hotplug: Implement cpuset tree traversal in a helper function
  CPU hotplug, cpusets, suspend: Don't modify cpusets during suspend/resume
  sched/x86: Remove broken power estimation
This commit is contained in:
Linus Torvalds 2012-07-26 13:08:01 -07:00
commit 79071638ce
9 changed files with 291 additions and 146 deletions
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2
arch/x86/kernel/cpu/Makefile
View file

@ -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

55
arch/x86/kernel/cpu/sched.c
View file

@ -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

4
include/linux/cpuset.h
View file

@ -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);
}

12
include/linux/init_task.h
View file

@ -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, \

6
include/linux/sched.h
View file

@ -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: */
@ -2721,7 +2725,7 @@ 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);

130
kernel/cpuset.c
View file

@ -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;

92
kernel/sched/core.c
View file

@ -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 @@ void partition_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
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);

113
kernel/sched/fair.c
View file

@ -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);
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 @@ static int load_balance(int this_cpu, struct rq *this_rq,
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 @@ static int load_balance(int this_cpu, struct rq *this_rq,
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 @@ static int load_balance(int this_cpu, struct rq *this_rq,
/*
* 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;
}
}

23
kernel/sched/sched.h
View file

@ -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 */