[GIT PULL] scheduler fixes

From: Ingo Molnar
Date: Sat Feb 15 2020 - 04:44:30 EST

Linus,

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

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

# HEAD: e9f5490c3574b435ce7fe7a71724aa3866babc7f sched/fair: Fix kernel-doc warning in attach_entity_load_avg()

Misc fixes all over the place:

- Fix NUMA over-balancing between lightly loaded nodes. This is fallout
of the big load-balancer rewrite.

- Fix the NOHZ remote loadavg update logic, which fixes anomalies
like reported 150 loadavg on mostly idle CPUs.

- Fix XFS performance/scalability

- Fix throttled groups unbound task-execution bug

- Fix PSI procfs boundary condition

- Fix the cpu.uclamp.{min,max} cgroup configuration write checks

- Fix DocBook annotations

- Fix RCU annotations

- Fix overly CPU-intensive housekeeper CPU logic loop on large CPU counts

Thanks,

Ingo

------------------>
Madhuparna Bhowmik (1):
sched/core: Annotate curr pointer in rq with __rcu

Mel Gorman (2):
sched/fair: Allow a small load imbalance between low utilisation SD_NUMA domains
sched/fair: Allow a per-CPU kthread waking a task to stack on the same CPU, to fix XFS performance regression

Peter Zijlstra (Intel) (1):
timers/nohz: Update NOHZ load in remote tick

Qais Yousef (1):
sched/uclamp: Reject negative values in cpu_uclamp_write()

Randy Dunlap (1):
sched/fair: Fix kernel-doc warning in attach_entity_load_avg()

Scott Wood (1):
sched/core: Don't skip remote tick for idle CPUs

Suren Baghdasaryan (1):
sched/psi: Fix OOB write when writing 0 bytes to PSI files

Vincent Guittot (1):
sched/fair: Prevent unlimited runtime on throttled group

Wanpeng Li (1):
sched/nohz: Optimize get_nohz_timer_target()


include/linux/sched/nohz.h | 2 ++
kernel/sched/core.c | 63 +++++++++++++++++++++++++---------------------
kernel/sched/fair.c | 56 +++++++++++++++++++++++++++++++----------
kernel/sched/loadavg.c | 33 ++++++++++++++++--------
kernel/sched/psi.c | 3 +++
kernel/sched/sched.h | 15 ++++++++++-
6 files changed, 119 insertions(+), 53 deletions(-)

diff --git a/include/linux/sched/nohz.h b/include/linux/sched/nohz.h
index 1abe91ff6e4a..6d67e9a5af6b 100644
--- a/include/linux/sched/nohz.h
+++ b/include/linux/sched/nohz.h
@@ -15,9 +15,11 @@ static inline void nohz_balance_enter_idle(int cpu) { }

#ifdef CONFIG_NO_HZ_COMMON
void calc_load_nohz_start(void);
+void calc_load_nohz_remote(struct rq *rq);
void calc_load_nohz_stop(void);
#else
static inline void calc_load_nohz_start(void) { }
+static inline void calc_load_nohz_remote(struct rq *rq) { }
static inline void calc_load_nohz_stop(void) { }
#endif /* CONFIG_NO_HZ_COMMON */

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fc1dfc007604..1a9983da4408 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -552,27 +552,32 @@ void resched_cpu(int cpu)
*/
int get_nohz_timer_target(void)
{
- int i, cpu = smp_processor_id();
+ int i, cpu = smp_processor_id(), default_cpu = -1;
struct sched_domain *sd;

- if (!idle_cpu(cpu) && housekeeping_cpu(cpu, HK_FLAG_TIMER))
- return cpu;
+ if (housekeeping_cpu(cpu, HK_FLAG_TIMER)) {
+ if (!idle_cpu(cpu))
+ return cpu;
+ default_cpu = cpu;
+ }

rcu_read_lock();
for_each_domain(cpu, sd) {
- for_each_cpu(i, sched_domain_span(sd)) {
+ for_each_cpu_and(i, sched_domain_span(sd),
+ housekeeping_cpumask(HK_FLAG_TIMER)) {
if (cpu == i)
continue;

- if (!idle_cpu(i) && housekeeping_cpu(i, HK_FLAG_TIMER)) {
+ if (!idle_cpu(i)) {
cpu = i;
goto unlock;
}
}
}

- if (!housekeeping_cpu(cpu, HK_FLAG_TIMER))
- cpu = housekeeping_any_cpu(HK_FLAG_TIMER);
+ if (default_cpu == -1)
+ default_cpu = housekeeping_any_cpu(HK_FLAG_TIMER);
+ cpu = default_cpu;
unlock:
rcu_read_unlock();
return cpu;
@@ -1442,17 +1447,6 @@ void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)

#ifdef CONFIG_SMP

-static inline bool is_per_cpu_kthread(struct task_struct *p)
-{
- if (!(p->flags & PF_KTHREAD))
- return false;
-
- if (p->nr_cpus_allowed != 1)
- return false;
-
- return true;
-}
-
/*
* Per-CPU kthreads are allowed to run on !active && online CPUs, see
* __set_cpus_allowed_ptr() and select_fallback_rq().
@@ -3669,28 +3663,32 @@ static void sched_tick_remote(struct work_struct *work)
* statistics and checks timeslices in a time-independent way, regardless
* of when exactly it is running.
*/
- if (idle_cpu(cpu) || !tick_nohz_tick_stopped_cpu(cpu))
+ if (!tick_nohz_tick_stopped_cpu(cpu))
goto out_requeue;

rq_lock_irq(rq, &rf);
curr = rq->curr;
- if (is_idle_task(curr) || cpu_is_offline(cpu))
+ if (cpu_is_offline(cpu))
goto out_unlock;

+ curr = rq->curr;
update_rq_clock(rq);
- delta = rq_clock_task(rq) - curr->se.exec_start;

- /*
- * Make sure the next tick runs within a reasonable
- * amount of time.
- */
- WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
+ if (!is_idle_task(curr)) {
+ /*
+ * Make sure the next tick runs within a reasonable
+ * amount of time.
+ */
+ delta = rq_clock_task(rq) - curr->se.exec_start;
+ WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
+ }
curr->sched_class->task_tick(rq, curr, 0);

+ calc_load_nohz_remote(rq);
out_unlock:
rq_unlock_irq(rq, &rf);
-
out_requeue:
+
/*
* Run the remote tick once per second (1Hz). This arbitrary
* frequency is large enough to avoid overload but short enough
@@ -7063,8 +7061,15 @@ void sched_move_task(struct task_struct *tsk)

if (queued)
enqueue_task(rq, tsk, queue_flags);
- if (running)
+ if (running) {
set_next_task(rq, tsk);
+ /*
+ * After changing group, the running task may have joined a
+ * throttled one but it's still the running task. Trigger a
+ * resched to make sure that task can still run.
+ */
+ resched_curr(rq);
+ }

task_rq_unlock(rq, tsk, &rf);
}
@@ -7260,7 +7265,7 @@ capacity_from_percent(char *buf)
&req.percent);
if (req.ret)
return req;
- if (req.percent > UCLAMP_PERCENT_SCALE) {
+ if ((u64)req.percent > UCLAMP_PERCENT_SCALE) {
req.ret = -ERANGE;
return req;
}
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fe4e0d775375..3c8a379c357e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3516,7 +3516,6 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
* attach_entity_load_avg - attach this entity to its cfs_rq load avg
* @cfs_rq: cfs_rq to attach to
* @se: sched_entity to attach
- * @flags: migration hints
*
* Must call update_cfs_rq_load_avg() before this, since we rely on
* cfs_rq->avg.last_update_time being current.
@@ -5912,6 +5911,20 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
(available_idle_cpu(prev) || sched_idle_cpu(prev)))
return prev;

+ /*
+ * Allow a per-cpu kthread to stack with the wakee if the
+ * kworker thread and the tasks previous CPUs are the same.
+ * The assumption is that the wakee queued work for the
+ * per-cpu kthread that is now complete and the wakeup is
+ * essentially a sync wakeup. An obvious example of this
+ * pattern is IO completions.
+ */
+ if (is_per_cpu_kthread(current) &&
+ prev == smp_processor_id() &&
+ this_rq()->nr_running <= 1) {
+ return prev;
+ }
+
/* Check a recently used CPU as a potential idle candidate: */
recent_used_cpu = p->recent_used_cpu;
if (recent_used_cpu != prev &&
@@ -8658,10 +8671,6 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
/*
* Try to use spare capacity of local group without overloading it or
* emptying busiest.
- * XXX Spreading tasks across NUMA nodes is not always the best policy
- * and special care should be taken for SD_NUMA domain level before
- * spreading the tasks. For now, load_balance() fully relies on
- * NUMA_BALANCING and fbq_classify_group/rq to override the decision.
*/
if (local->group_type == group_has_spare) {
if (busiest->group_type > group_fully_busy) {
@@ -8701,16 +8710,37 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
env->migration_type = migrate_task;
lsub_positive(&nr_diff, local->sum_nr_running);
env->imbalance = nr_diff >> 1;
- return;
- }
+ } else {

- /*
- * If there is no overload, we just want to even the number of
- * idle cpus.
- */
- env->migration_type = migrate_task;
- env->imbalance = max_t(long, 0, (local->idle_cpus -
+ /*
+ * If there is no overload, we just want to even the number of
+ * idle cpus.
+ */
+ env->migration_type = migrate_task;
+ env->imbalance = max_t(long, 0, (local->idle_cpus -
busiest->idle_cpus) >> 1);
+ }
+
+ /* Consider allowing a small imbalance between NUMA groups */
+ if (env->sd->flags & SD_NUMA) {
+ unsigned int imbalance_min;
+
+ /*
+ * Compute an allowed imbalance based on a simple
+ * pair of communicating tasks that should remain
+ * local and ignore them.
+ *
+ * NOTE: Generally this would have been based on
+ * the domain size and this was evaluated. However,
+ * the benefit is similar across a range of workloads
+ * and machines but scaling by the domain size adds
+ * the risk that lower domains have to be rebalanced.
+ */
+ imbalance_min = 2;
+ if (busiest->sum_nr_running <= imbalance_min)
+ env->imbalance = 0;
+ }
+
return;
}

diff --git a/kernel/sched/loadavg.c b/kernel/sched/loadavg.c
index 28a516575c18..de22da666ac7 100644
--- a/kernel/sched/loadavg.c
+++ b/kernel/sched/loadavg.c
@@ -231,16 +231,11 @@ static inline int calc_load_read_idx(void)
return calc_load_idx & 1;
}

-void calc_load_nohz_start(void)
+static void calc_load_nohz_fold(struct rq *rq)
{
- struct rq *this_rq = this_rq();
long delta;

- /*
- * We're going into NO_HZ mode, if there's any pending delta, fold it
- * into the pending NO_HZ delta.
- */
- delta = calc_load_fold_active(this_rq, 0);
+ delta = calc_load_fold_active(rq, 0);
if (delta) {
int idx = calc_load_write_idx();

@@ -248,6 +243,24 @@ void calc_load_nohz_start(void)
}
}

+void calc_load_nohz_start(void)
+{
+ /*
+ * We're going into NO_HZ mode, if there's any pending delta, fold it
+ * into the pending NO_HZ delta.
+ */
+ calc_load_nohz_fold(this_rq());
+}
+
+/*
+ * Keep track of the load for NOHZ_FULL, must be called between
+ * calc_load_nohz_{start,stop}().
+ */
+void calc_load_nohz_remote(struct rq *rq)
+{
+ calc_load_nohz_fold(rq);
+}
+
void calc_load_nohz_stop(void)
{
struct rq *this_rq = this_rq();
@@ -268,7 +281,7 @@ void calc_load_nohz_stop(void)
this_rq->calc_load_update += LOAD_FREQ;
}

-static long calc_load_nohz_fold(void)
+static long calc_load_nohz_read(void)
{
int idx = calc_load_read_idx();
long delta = 0;
@@ -323,7 +336,7 @@ static void calc_global_nohz(void)
}
#else /* !CONFIG_NO_HZ_COMMON */

-static inline long calc_load_nohz_fold(void) { return 0; }
+static inline long calc_load_nohz_read(void) { return 0; }
static inline void calc_global_nohz(void) { }

#endif /* CONFIG_NO_HZ_COMMON */
@@ -346,7 +359,7 @@ void calc_global_load(unsigned long ticks)
/*
* Fold the 'old' NO_HZ-delta to include all NO_HZ CPUs.
*/
- delta = calc_load_nohz_fold();
+ delta = calc_load_nohz_read();
if (delta)
atomic_long_add(delta, &calc_load_tasks);

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index db7b50bba3f1..38ccd49b9bf6 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1199,6 +1199,9 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
if (static_branch_likely(&psi_disabled))
return -EOPNOTSUPP;

+ if (!nbytes)
+ return -EINVAL;
+
buf_size = min(nbytes, sizeof(buf));
if (copy_from_user(buf, user_buf, buf_size))
return -EFAULT;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 1a88dc8ad11b..9ea647835fd6 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -896,7 +896,7 @@ struct rq {
*/
unsigned long nr_uninterruptible;

- struct task_struct *curr;
+ struct task_struct __rcu *curr;
struct task_struct *idle;
struct task_struct *stop;
unsigned long next_balance;
@@ -2479,3 +2479,16 @@ static inline void membarrier_switch_mm(struct rq *rq,
{
}
#endif
+
+#ifdef CONFIG_SMP
+static inline bool is_per_cpu_kthread(struct task_struct *p)
+{
+ if (!(p->flags & PF_KTHREAD))
+ return false;
+
+ if (p->nr_cpus_allowed != 1)
+ return false;
+
+ return true;
+}
+#endif