sched: Clean up scheduler_ipi()

The scheduler IPI has grown weird and wonderful over the years, time
for spring cleaning.

Move all the non-trivial stuff out of it and into a regular smp function
call IPI. This then reduces the schedule_ipi() to most of it's former NOP
glory and ensures to keep the interrupt vector lean and mean.

Aside of that avoiding the full irq_enter() in the x86 IPI implementation
is incorrect as scheduler_ipi() can be instrumented. To work around that
scheduler_ipi() had an irq_enter/exit() hack when heavy work was
pending. This is gone now.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Link: https://lkml.kernel.org/r/20200505134058.361859938@linutronix.de

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b58efb1..cd2070d 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -219,6 +219,13 @@ void update_rq_clock(struct rq *rq)
        update_rq_clock_task(rq, delta);
 }
 
+static inline void
+rq_csd_init(struct rq *rq, call_single_data_t *csd, smp_call_func_t func)
+{
+       csd->flags = 0;
+       csd->func = func;
+       csd->info = rq;
+}
 
 #ifdef CONFIG_SCHED_HRTICK
 /*
@@ -314,16 +321,14 @@ void hrtick_start(struct rq *rq, u64 delay)
        hrtimer_start(&rq->hrtick_timer, ns_to_ktime(delay),
                      HRTIMER_MODE_REL_PINNED_HARD);
 }
+
 #endif /* CONFIG_SMP */
 
 static void hrtick_rq_init(struct rq *rq)
 {
 #ifdef CONFIG_SMP
-       rq->hrtick_csd.flags = 0;
-       rq->hrtick_csd.func = __hrtick_start;
-       rq->hrtick_csd.info = rq;
+       rq_csd_init(rq, &rq->hrtick_csd, __hrtick_start);
 #endif
-
        hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
        rq->hrtick_timer.function = hrtick;
 }
@@ -650,6 +655,16 @@ static inline bool got_nohz_idle_kick(void)
        return false;
 }
 
+static void nohz_csd_func(void *info)
+{
+       struct rq *rq = info;
+
+       if (got_nohz_idle_kick()) {
+               rq->idle_balance = 1;
+               raise_softirq_irqoff(SCHED_SOFTIRQ);
+       }
+}
+
 #else /* CONFIG_NO_HZ_COMMON */
 
 static inline bool got_nohz_idle_kick(void)
@@ -2292,6 +2307,11 @@ void sched_ttwu_pending(void)
        rq_unlock_irqrestore(rq, &rf);
 }
 
+static void wake_csd_func(void *info)
+{
+       sched_ttwu_pending();
+}
+
 void scheduler_ipi(void)
 {
        /*
@@ -2300,34 +2320,6 @@ void scheduler_ipi(void)
         * this IPI.
         */
        preempt_fold_need_resched();
-
-       if (llist_empty(&this_rq()->wake_list) && !got_nohz_idle_kick())
-               return;
-
-       /*
-        * Not all reschedule IPI handlers call irq_enter/irq_exit, since
-        * traditionally all their work was done from the interrupt return
-        * path. Now that we actually do some work, we need to make sure
-        * we do call them.
-        *
-        * Some archs already do call them, luckily irq_enter/exit nest
-        * properly.
-        *
-        * Arguably we should visit all archs and update all handlers,
-        * however a fair share of IPIs are still resched only so this would
-        * somewhat pessimize the simple resched case.
-        */
-       irq_enter();
-       sched_ttwu_pending();
-
-       /*
-        * Check if someone kicked us for doing the nohz idle load balance.
-        */
-       if (unlikely(got_nohz_idle_kick())) {
-               this_rq()->idle_balance = 1;
-               raise_softirq_irqoff(SCHED_SOFTIRQ);
-       }
-       irq_exit();
 }
 
 static void ttwu_queue_remote(struct task_struct *p, int cpu, int wake_flags)
@@ -2336,9 +2328,9 @@ static void ttwu_queue_remote(struct task_struct *p, int cpu, int wake_flags)
 
        p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);
 
-       if (llist_add(&p->wake_entry, &cpu_rq(cpu)->wake_list)) {
+       if (llist_add(&p->wake_entry, &rq->wake_list)) {
                if (!set_nr_if_polling(rq->idle))
-                       smp_send_reschedule(cpu);
+                       smp_call_function_single_async(cpu, &rq->wake_csd);
                else
                        trace_sched_wake_idle_without_ipi(cpu);
        }
@@ -6693,12 +6685,16 @@ void __init sched_init(void)
                rq->avg_idle = 2*sysctl_sched_migration_cost;
                rq->max_idle_balance_cost = sysctl_sched_migration_cost;
 
+               rq_csd_init(rq, &rq->wake_csd, wake_csd_func);
+
                INIT_LIST_HEAD(&rq->cfs_tasks);
 
                rq_attach_root(rq, &def_root_domain);
 #ifdef CONFIG_NO_HZ_COMMON
                rq->last_blocked_load_update_tick = jiffies;
                atomic_set(&rq->nohz_flags, 0);
+
+               rq_csd_init(rq, &rq->nohz_csd, nohz_csd_func);
 #endif
 #endif /* CONFIG_SMP */
                hrtick_rq_init(rq);

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 46b7bd4..6b7f147 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10000,12 +10000,11 @@ static void kick_ilb(unsigned int flags)
                return;
 
        /*
-        * Use smp_send_reschedule() instead of resched_cpu().
-        * This way we generate a sched IPI on the target CPU which
+        * This way we generate an IPI on the target CPU which
         * is idle. And the softirq performing nohz idle load balance
         * will be run before returning from the IPI.
         */
-       smp_send_reschedule(ilb_cpu);
+       smp_call_function_single_async(ilb_cpu, &cpu_rq(ilb_cpu)->nohz_csd);
 }
 
 /*

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 978c6fa..21416b3 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -889,9 +889,10 @@ struct rq {
 #ifdef CONFIG_SMP
        unsigned long           last_blocked_load_update_tick;
        unsigned int            has_blocked_load;
+       call_single_data_t      nohz_csd;
 #endif /* CONFIG_SMP */
        unsigned int            nohz_tick_stopped;
-       atomic_t nohz_flags;
+       atomic_t                nohz_flags;
 #endif /* CONFIG_NO_HZ_COMMON */
 
        unsigned long           nr_load_updates;
@@ -978,7 +979,7 @@ struct rq {
 
        /* This is used to determine avg_idle's max value */
        u64                     max_idle_balance_cost;
-#endif
+#endif /* CONFIG_SMP */
 
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
        u64                     prev_irq_time;
@@ -1020,6 +1021,7 @@ struct rq {
 #endif
 
 #ifdef CONFIG_SMP
+       call_single_data_t      wake_csd;
        struct llist_head       wake_list;
 #endif