Add WF_CURRENT_CPU wake flag that advices the scheduler to
move the wakee to the current CPU. This is useful for fast on-CPU
context switching use cases such as UMCG.
In addition, make ttwu external rather than static so that
the flag could be passed to it from outside of sched/core.c.
Signed-off-by: Peter Oskolkov <posk@xxxxxxxxxx>
---
kernel/sched/core.c | 3 +--
kernel/sched/fair.c | 4 ++++
kernel/sched/sched.h | 15 +++++++++------
3 files changed, 14 insertions(+), 8 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index beaa8be6241e..5344aa0afe5a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3977,8 +3977,7 @@ bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success)
* Return: %true if @p->state changes (an actual wakeup was done),
* %false otherwise.
*/
-static int
-try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
+int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
{
unsigned long flags;
int cpu, success = 0;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 884f29d07963..399422e6479b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6890,6 +6890,10 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
if (wake_flags & WF_TTWU) {
record_wakee(p);
+ if ((wake_flags & WF_CURRENT_CPU) &&
+ cpumask_test_cpu(cpu, p->cpus_ptr))
+ return cpu;
+
if (sched_energy_enabled()) {
new_cpu = find_energy_efficient_cpu(p, prev_cpu);
if (new_cpu >= 0)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index eb971151e7e4..5e1ecf89c12b 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2052,13 +2052,14 @@ static inline int task_on_rq_migrating(struct task_struct *p)
}
/* Wake flags. The first three directly map to some SD flag value */
-#define WF_EXEC 0x02 /* Wakeup after exec; maps to SD_BALANCE_EXEC */
-#define WF_FORK 0x04 /* Wakeup after fork; maps to SD_BALANCE_FORK */
-#define WF_TTWU 0x08 /* Wakeup; maps to SD_BALANCE_WAKE */
+#define WF_EXEC 0x02 /* Wakeup after exec; maps to SD_BALANCE_EXEC */
+#define WF_FORK 0x04 /* Wakeup after fork; maps to SD_BALANCE_FORK */
+#define WF_TTWU 0x08 /* Wakeup; maps to SD_BALANCE_WAKE */
-#define WF_SYNC 0x10 /* Waker goes to sleep after wakeup */
-#define WF_MIGRATED 0x20 /* Internal use, task got migrated */
-#define WF_ON_CPU 0x40 /* Wakee is on_cpu */
+#define WF_SYNC 0x10 /* Waker goes to sleep after wakeup */
+#define WF_MIGRATED 0x20 /* Internal use, task got migrated */
+#define WF_ON_CPU 0x40 /* Wakee is on_cpu */
+#define WF_CURRENT_CPU 0x80 /* Prefer to move the wakee to the current CPU. */
#ifdef CONFIG_SMP
static_assert(WF_EXEC == SD_BALANCE_EXEC);
@@ -3076,6 +3077,8 @@ static inline bool is_per_cpu_kthread(struct task_struct *p)
extern void swake_up_all_locked(struct swait_queue_head *q);
extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait);
+extern int try_to_wake_up(struct task_struct *tsk, unsigned int state, int wake_flags);
+
#ifdef CONFIG_PREEMPT_DYNAMIC
extern int preempt_dynamic_mode;
extern int sched_dynamic_mode(const char *str);
--
2.25.1
