When a interrupt affinity mask targets multiple CPUs, the
RT scheduler selects a runqueue for RT task corresponding
to a threaded interrupt handler without consideration of
where the interrupt is actually gets delivered. It leads
to a suboptimal condition when a hardware interrupt handler
executes on one CPU while the threaded interrupt handler
executes on another CPU.
This fix alters the behaviour of threaded handler wake-ups
by getting priority to a CPU where the hardware interrupt
handler is executing. As result, most of the time both
halves of interrupt handling are kept local.
Signed-off-by: Alexander Gordeev <agord...@redhat.com>
---
include/linux/sched.h | 2 ++
kernel/irq/handle.c | 2 +-
kernel/sched/core.c | 5 +++++
kernel/sched/rt.c | 27 +++++++++++++++++++--------
4 files changed, 27 insertions(+), 9 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 206bb08..1d59efa 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1061,6 +1061,7 @@ struct sched_domain;
#define WF_SYNC 0x01 /* waker goes to sleep after
wakup */
#define WF_FORK 0x02 /* child wakeup after fork */
#define WF_MIGRATED 0x04 /* internal use, task got migrated */
+#define WF_LOCAL 0x08 /* try to wake up locally */
#define ENQUEUE_WAKEUP 1
#define ENQUEUE_HEAD 2
@@ -2207,6 +2208,7 @@ extern void xtime_update(unsigned long ticks);
extern int wake_up_state(struct task_struct *tsk, unsigned int state);
extern int wake_up_process(struct task_struct *tsk);
+extern int wake_up_local(struct task_struct *tsk);
extern void wake_up_new_task(struct task_struct *tsk);
#ifdef CONFIG_SMP
extern void kick_process(struct task_struct *tsk);
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index 131ca17..fe97d0c 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -126,7 +126,7 @@ static void irq_wake_thread(struct irq_desc *desc, struct
irqaction *action)
*/
atomic_inc(&desc->threads_active);
- wake_up_process(action->thread);
+ wake_up_local(action->thread);
}
irqreturn_t
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 257002c..38413f6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1527,6 +1527,11 @@ int wake_up_process(struct task_struct *p)
}
EXPORT_SYMBOL(wake_up_process);
+int wake_up_local(struct task_struct *p)
+{
+ return try_to_wake_up(p, TASK_ALL, WF_LOCAL);
+}
+
int wake_up_state(struct task_struct *p, unsigned int state)
{
return try_to_wake_up(p, state, 0);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 418feb0..de16e16 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1234,7 +1234,7 @@ static void yield_task_rt(struct rq *rq)
}
#ifdef CONFIG_SMP
-static int find_lowest_rq(struct task_struct *task);
+static int find_lowest_rq(struct task_struct *task, bool prefer_this_cpu);
static int
select_task_rq_rt(struct task_struct *p, int sd_flag, int flags)
@@ -1242,6 +1242,7 @@ select_task_rq_rt(struct task_struct *p, int sd_flag, int
flags)
struct task_struct *curr;
struct rq *rq;
int cpu;
+ bool prefer_this_cpu = flags & WF_LOCAL;
cpu = task_cpu(p);
@@ -1258,6 +1259,11 @@ select_task_rq_rt(struct task_struct *p, int sd_flag,
int flags)
curr = ACCESS_ONCE(rq->curr); /* unlocked access */
/*
+ * If this RT task is a threaded interrupt handler, then
+ * it is being awaken from the hardware interrupt handler.
+ * In this case try to keep hardware and threaded interrupt
+ * handlers as close as possible and wake it up on this CPU.
+ *
* If the current task on @p's runqueue is an RT task, then
* try to see if we can wake this RT task up on another
* runqueue. Otherwise simply start this RT task
@@ -1279,11 +1285,12 @@ select_task_rq_rt(struct task_struct *p, int sd_flag,
int flags)
* This test is optimistic, if we get it wrong the load-balancer
* will have to sort it out.
*/
- if (curr && unlikely(rt_task(curr)) &&
- (curr->nr_cpus_allowed < 2 ||
- curr->prio <= p->prio) &&
- (p->nr_cpus_allowed > 1)) {
- int target = find_lowest_rq(p);
+ if (prefer_this_cpu ||
+ (curr && unlikely(rt_task(curr)) &&
+ (curr->nr_cpus_allowed < 2 ||
+ curr->prio <= p->prio) &&
+ (p->nr_cpus_allowed > 1))) {
+ int target = find_lowest_rq(p, prefer_this_cpu);
if (target != -1)
cpu = target;
@@ -1473,7 +1480,7 @@ next_idx:
static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask);
-static int find_lowest_rq(struct task_struct *task)
+static int find_lowest_rq(struct task_struct *task, bool prefer_this_cpu)
{
struct sched_domain *sd;
struct cpumask *lowest_mask = __get_cpu_var(local_cpu_mask);
@@ -1495,9 +1502,13 @@ static int find_lowest_rq(struct task_struct *task)
* lowest priority tasks in the system. Now we want to elect
* the best one based on our affinity and topology.
*
+ * If asked explicitly, try to pick up this cpu.
+ *
* We prioritize the last cpu that the task executed on since
* it is most likely cache-hot in that location.
*/
+ if (prefer_this_cpu && cpumask_test_cpu(this_cpu, lowest_mask))
+ return this_cpu;
if (cpumask_test_cpu(cpu, lowest_mask))
return cpu;
@@ -1555,7 +1566,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct
*task, struct rq *rq)
int cpu;
for (tries = 0; tries < RT_MAX_TRIES; tries++) {
- cpu = find_lowest_rq(task);
+ cpu = find_lowest_rq(task, false);
if ((cpu == -1) || (cpu == rq->cpu))
break;
--
1.7.7.6
--
Regards,
Alexander Gordeev
agord...@redhat.com
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