[PATCH 3/9] sched: Simplify: migrate_swap_stop()

From: Peter Zijlstra
Date: Tue Aug 01 2023 - 17:25:07 EST


Use guards to reduce gotos and simplify control flow.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
kernel/sched/core.c | 23 +++++++----------------
kernel/sched/sched.h | 20 ++++++++++++++++++++
2 files changed, 27 insertions(+), 16 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3258,7 +3258,6 @@ static int migrate_swap_stop(void *data)
{
struct migration_swap_arg *arg = data;
struct rq *src_rq, *dst_rq;
- int ret = -EAGAIN;

if (!cpu_active(arg->src_cpu) || !cpu_active(arg->dst_cpu))
return -EAGAIN;
@@ -3266,33 +3265,25 @@ static int migrate_swap_stop(void *data)
src_rq = cpu_rq(arg->src_cpu);
dst_rq = cpu_rq(arg->dst_cpu);

- double_raw_lock(&arg->src_task->pi_lock,
- &arg->dst_task->pi_lock);
- double_rq_lock(src_rq, dst_rq);
+ guard(double_raw_spinlock)(&arg->src_task->pi_lock, &arg->dst_task->pi_lock);
+ guard(double_rq_lock)(src_rq, dst_rq);

if (task_cpu(arg->dst_task) != arg->dst_cpu)
- goto unlock;
+ return -EAGAIN;

if (task_cpu(arg->src_task) != arg->src_cpu)
- goto unlock;
+ return -EAGAIN;

if (!cpumask_test_cpu(arg->dst_cpu, arg->src_task->cpus_ptr))
- goto unlock;
+ return -EAGAIN;

if (!cpumask_test_cpu(arg->src_cpu, arg->dst_task->cpus_ptr))
- goto unlock;
+ return -EAGAIN;

__migrate_swap_task(arg->src_task, arg->dst_cpu);
__migrate_swap_task(arg->dst_task, arg->src_cpu);

- ret = 0;
-
-unlock:
- double_rq_unlock(src_rq, dst_rq);
- raw_spin_unlock(&arg->dst_task->pi_lock);
- raw_spin_unlock(&arg->src_task->pi_lock);
-
- return ret;
+ return 0;
}

/*
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2572,6 +2572,12 @@ static inline void double_rq_clock_clear
static inline void double_rq_clock_clear_update(struct rq *rq1, struct rq *rq2) {}
#endif

+#define DEFINE_LOCK_GUARD_2(name, type, _lock, _unlock, ...) \
+__DEFINE_UNLOCK_GUARD(name, type, _unlock, type *lock2; __VA_ARGS__) \
+static inline class_##name##_t class_##name##_constructor(type *lock, type *lock2) \
+{ class_##name##_t _t = { .lock = lock, .lock2 = lock2 }, *_T = &_t; \
+ _lock; return _t; }
+
#ifdef CONFIG_SMP

static inline bool rq_order_less(struct rq *rq1, struct rq *rq2)
@@ -2701,6 +2707,16 @@ static inline void double_raw_lock(raw_s
raw_spin_lock_nested(l2, SINGLE_DEPTH_NESTING);
}

+static inline void double_raw_unlock(raw_spinlock_t *l1, raw_spinlock_t *l2)
+{
+ raw_spin_unlock(l1);
+ raw_spin_unlock(l2);
+}
+
+DEFINE_LOCK_GUARD_2(double_raw_spinlock, raw_spinlock_t,
+ double_raw_lock(_T->lock, _T->lock2),
+ double_raw_unlock(_T->lock, _T->lock2))
+
/*
* double_rq_unlock - safely unlock two runqueues
*
@@ -2758,6 +2774,10 @@ static inline void double_rq_unlock(stru

#endif

+DEFINE_LOCK_GUARD_2(double_rq_lock, struct rq,
+ double_rq_lock(_T->lock, _T->lock2),
+ double_rq_unlock(_T->lock, _T->lock2))
+
extern struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq);
extern struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq);