diff options
Diffstat (limited to 'debian/patches-rt/0005-sched-core-Wait-for-tasks-being-pushed-away-on-hotpl.patch')
| -rw-r--r-- | debian/patches-rt/0005-sched-core-Wait-for-tasks-being-pushed-away-on-hotpl.patch | 124 |
1 files changed, 124 insertions, 0 deletions
diff --git a/debian/patches-rt/0005-sched-core-Wait-for-tasks-being-pushed-away-on-hotpl.patch b/debian/patches-rt/0005-sched-core-Wait-for-tasks-being-pushed-away-on-hotpl.patch new file mode 100644 index 000000000..abd6b3875 --- /dev/null +++ b/debian/patches-rt/0005-sched-core-Wait-for-tasks-being-pushed-away-on-hotpl.patch @@ -0,0 +1,124 @@ +From 94b59ab31222fc252603987e1ee316264426a015 Mon Sep 17 00:00:00 2001 +From: Thomas Gleixner <tglx@linutronix.de> +Date: Fri, 23 Oct 2020 12:12:02 +0200 +Subject: [PATCH 005/323] sched/core: Wait for tasks being pushed away on + hotplug +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz + +RT kernels need to ensure that all tasks which are not per CPU kthreads +have left the outgoing CPU to guarantee that no tasks are force migrated +within a migrate disabled section. + +There is also some desire to (ab)use fine grained CPU hotplug control to +clear a CPU from active state to force migrate tasks which are not per CPU +kthreads away for power control purposes. + +Add a mechanism which waits until all tasks which should leave the CPU +after the CPU active flag is cleared have moved to a different online CPU. + +Signed-off-by: Thomas Gleixner <tglx@linutronix.de> +Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/sched/core.c | 40 +++++++++++++++++++++++++++++++++++++++- + kernel/sched/sched.h | 4 ++++ + 2 files changed, 43 insertions(+), 1 deletion(-) + +diff --git a/kernel/sched/core.c b/kernel/sched/core.c +index 32c3acef5781..b902755615d7 100644 +--- a/kernel/sched/core.c ++++ b/kernel/sched/core.c +@@ -6896,8 +6896,21 @@ static void balance_push(struct rq *rq) + * Both the cpu-hotplug and stop task are in this case and are + * required to complete the hotplug process. + */ +- if (is_per_cpu_kthread(push_task)) ++ if (is_per_cpu_kthread(push_task)) { ++ /* ++ * If this is the idle task on the outgoing CPU try to wake ++ * up the hotplug control thread which might wait for the ++ * last task to vanish. The rcuwait_active() check is ++ * accurate here because the waiter is pinned on this CPU ++ * and can't obviously be running in parallel. ++ */ ++ if (!rq->nr_running && rcuwait_active(&rq->hotplug_wait)) { ++ raw_spin_unlock(&rq->lock); ++ rcuwait_wake_up(&rq->hotplug_wait); ++ raw_spin_lock(&rq->lock); ++ } + return; ++ } + + get_task_struct(push_task); + /* +@@ -6928,6 +6941,20 @@ static void balance_push_set(int cpu, bool on) + rq_unlock_irqrestore(rq, &rf); + } + ++/* ++ * Invoked from a CPUs hotplug control thread after the CPU has been marked ++ * inactive. All tasks which are not per CPU kernel threads are either ++ * pushed off this CPU now via balance_push() or placed on a different CPU ++ * during wakeup. Wait until the CPU is quiescent. ++ */ ++static void balance_hotplug_wait(void) ++{ ++ struct rq *rq = this_rq(); ++ ++ rcuwait_wait_event(&rq->hotplug_wait, rq->nr_running == 1, ++ TASK_UNINTERRUPTIBLE); ++} ++ + #else + + static inline void balance_push(struct rq *rq) +@@ -6938,6 +6965,10 @@ static inline void balance_push_set(int cpu, bool on) + { + } + ++static inline void balance_hotplug_wait(void) ++{ ++} ++ + #endif /* CONFIG_HOTPLUG_CPU */ + + void set_rq_online(struct rq *rq) +@@ -7094,6 +7125,10 @@ int sched_cpu_deactivate(unsigned int cpu) + return ret; + } + sched_domains_numa_masks_clear(cpu); ++ ++ /* Wait for all non per CPU kernel threads to vanish. */ ++ balance_hotplug_wait(); ++ + return 0; + } + +@@ -7334,6 +7369,9 @@ void __init sched_init(void) + + rq_csd_init(rq, &rq->nohz_csd, nohz_csd_func); + #endif ++#ifdef CONFIG_HOTPLUG_CPU ++ rcuwait_init(&rq->hotplug_wait); ++#endif + #endif /* CONFIG_SMP */ + hrtick_rq_init(rq); + atomic_set(&rq->nr_iowait, 0); +diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h +index 81dc4212423a..a72464d370cd 100644 +--- a/kernel/sched/sched.h ++++ b/kernel/sched/sched.h +@@ -1007,6 +1007,10 @@ struct rq { + + /* This is used to determine avg_idle's max value */ + u64 max_idle_balance_cost; ++ ++#ifdef CONFIG_HOTPLUG_CPU ++ struct rcuwait hotplug_wait; ++#endif + #endif /* CONFIG_SMP */ + + #ifdef CONFIG_IRQ_TIME_ACCOUNTING +-- +2.43.0 + |