Merge tag 'sched-core-2020-06-02' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler updates from Ingo Molnar:
 "The changes in this cycle are:

   - Optimize the task wakeup CPU selection logic, to improve
     scalability and reduce wakeup latency spikes

   - PELT enhancements

   - CFS bandwidth handling fixes

   - Optimize the wakeup path by remove rq->wake_list and replacing it
     with ->ttwu_pending

   - Optimize IPI cross-calls by making flush_smp_call_function_queue()
     process sync callbacks first.

   - Misc fixes and enhancements"

* tag 'sched-core-2020-06-02' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (36 commits)
  irq_work: Define irq_work_single() on !CONFIG_IRQ_WORK too
  sched/headers: Split out open-coded prototypes into kernel/sched/smp.h
  sched: Replace rq::wake_list
  sched: Add rq::ttwu_pending
  irq_work, smp: Allow irq_work on call_single_queue
  smp: Optimize send_call_function_single_ipi()
  smp: Move irq_work_run() out of flush_smp_call_function_queue()
  smp: Optimize flush_smp_call_function_queue()
  sched: Fix smp_call_function_single_async() usage for ILB
  sched/core: Offload wakee task activation if it the wakee is descheduling
  sched/core: Optimize ttwu() spinning on p->on_cpu
  sched: Defend cfs and rt bandwidth quota against overflow
  sched/cpuacct: Fix charge cpuacct.usage_sys
  sched/fair: Replace zero-length array with flexible-array
  sched/pelt: Sync util/runnable_sum with PELT window when propagating
  sched/cpuacct: Use __this_cpu_add() instead of this_cpu_ptr()
  sched/fair: Optimize enqueue_task_fair()
  sched: Make scheduler_ipi inline
  sched: Clean up scheduler_ipi()
  sched/core: Simplify sched_init()
  ...

include/linux/irq_work.h

@@ -13,6 +13,8 @@
  * busy      NULL, 2 -> {free, claimed} : callback in progress, can be claimed
  */
 
+/* flags share CSD_FLAG_ space */
+
 #define IRQ_WORK_PENDING	BIT(0)
 #define IRQ_WORK_BUSY		BIT(1)
 
@@ -23,9 +25,12 @@
 
 #define IRQ_WORK_CLAIMED	(IRQ_WORK_PENDING | IRQ_WORK_BUSY)
 
+/*
+ * structure shares layout with single_call_data_t.
+ */
 struct irq_work {
-	atomic_t flags;
 	struct llist_node llnode;
+	atomic_t flags;
 	void (*func)(struct irq_work *);
 };
 
@@ -53,9 +58,11 @@ void irq_work_sync(struct irq_work *work);
 
 void irq_work_run(void);
 bool irq_work_needs_cpu(void);
+void irq_work_single(void *arg);
 #else
 static inline bool irq_work_needs_cpu(void) { return false; }
 static inline void irq_work_run(void) { }
+static inline void irq_work_single(void *arg) { }
 #endif
 
 #endif /* _LINUX_IRQ_WORK_H */

include/linux/sched.h

@@ -654,6 +654,7 @@ struct task_struct {
 
 #ifdef CONFIG_SMP
 	struct llist_node		wake_entry;
+	unsigned int			wake_entry_type;
 	int				on_cpu;
 #ifdef CONFIG_THREAD_INFO_IN_TASK
 	/* Current CPU: */
@@ -1730,7 +1731,15 @@ extern char *__get_task_comm(char *to, size_t len, struct task_struct *tsk);
 })
 
 #ifdef CONFIG_SMP
-void scheduler_ipi(void);
+static __always_inline void scheduler_ipi(void)
+{
+	/*
+	 * Fold TIF_NEED_RESCHED into the preempt_count; anybody setting
+	 * TIF_NEED_RESCHED remotely (for the first time) will also send
+	 * this IPI.
+	 */
+	preempt_fold_need_resched();
+}
 extern unsigned long wait_task_inactive(struct task_struct *, long match_state);
 #else
 static inline void scheduler_ipi(void) { }

include/linux/sched/mm.h

@@ -49,6 +49,8 @@ static inline void mmdrop(struct mm_struct *mm)
 		__mmdrop(mm);
 }
 
+void mmdrop(struct mm_struct *mm);
+
 /*
  * This has to be called after a get_task_mm()/mmget_not_zero()
  * followed by taking the mmap_sem for writing before modifying the

include/linux/sched/topology.h

@@ -11,21 +11,20 @@
  */
 #ifdef CONFIG_SMP
 
-#define SD_LOAD_BALANCE		0x0001	/* Do load balancing on this domain. */
-#define SD_BALANCE_NEWIDLE	0x0002	/* Balance when about to become idle */
-#define SD_BALANCE_EXEC		0x0004	/* Balance on exec */
-#define SD_BALANCE_FORK		0x0008	/* Balance on fork, clone */
-#define SD_BALANCE_WAKE		0x0010  /* Balance on wakeup */
-#define SD_WAKE_AFFINE		0x0020	/* Wake task to waking CPU */
-#define SD_ASYM_CPUCAPACITY	0x0040  /* Domain members have different CPU capacities */
-#define SD_SHARE_CPUCAPACITY	0x0080	/* Domain members share CPU capacity */
-#define SD_SHARE_POWERDOMAIN	0x0100	/* Domain members share power domain */
-#define SD_SHARE_PKG_RESOURCES	0x0200	/* Domain members share CPU pkg resources */
-#define SD_SERIALIZE		0x0400	/* Only a single load balancing instance */
-#define SD_ASYM_PACKING		0x0800  /* Place busy groups earlier in the domain */
-#define SD_PREFER_SIBLING	0x1000	/* Prefer to place tasks in a sibling domain */
-#define SD_OVERLAP		0x2000	/* sched_domains of this level overlap */
-#define SD_NUMA			0x4000	/* cross-node balancing */
+#define SD_BALANCE_NEWIDLE	0x0001	/* Balance when about to become idle */
+#define SD_BALANCE_EXEC		0x0002	/* Balance on exec */
+#define SD_BALANCE_FORK		0x0004	/* Balance on fork, clone */
+#define SD_BALANCE_WAKE		0x0008  /* Balance on wakeup */
+#define SD_WAKE_AFFINE		0x0010	/* Wake task to waking CPU */
+#define SD_ASYM_CPUCAPACITY	0x0020  /* Domain members have different CPU capacities */
+#define SD_SHARE_CPUCAPACITY	0x0040	/* Domain members share CPU capacity */
+#define SD_SHARE_POWERDOMAIN	0x0080	/* Domain members share power domain */
+#define SD_SHARE_PKG_RESOURCES	0x0100	/* Domain members share CPU pkg resources */
+#define SD_SERIALIZE		0x0200	/* Only a single load balancing instance */
+#define SD_ASYM_PACKING		0x0400  /* Place busy groups earlier in the domain */
+#define SD_PREFER_SIBLING	0x0800	/* Prefer to place tasks in a sibling domain */
+#define SD_OVERLAP		0x1000	/* sched_domains of this level overlap */
+#define SD_NUMA			0x2000	/* cross-node balancing */
 
 #ifdef CONFIG_SCHED_SMT
 static inline int cpu_smt_flags(void)

include/linux/smp.h

@@ -16,17 +16,39 @@
 
 typedef void (*smp_call_func_t)(void *info);
 typedef bool (*smp_cond_func_t)(int cpu, void *info);
+
+enum {
+	CSD_FLAG_LOCK		= 0x01,
+
+	/* IRQ_WORK_flags */
+
+	CSD_TYPE_ASYNC		= 0x00,
+	CSD_TYPE_SYNC		= 0x10,
+	CSD_TYPE_IRQ_WORK	= 0x20,
+	CSD_TYPE_TTWU		= 0x30,
+	CSD_FLAG_TYPE_MASK	= 0xF0,
+};
+
+/*
+ * structure shares (partial) layout with struct irq_work
+ */
 struct __call_single_data {
 	struct llist_node llist;
+	unsigned int flags;
 	smp_call_func_t func;
 	void *info;
-	unsigned int flags;
 };
 
 /* Use __aligned() to avoid to use 2 cache lines for 1 csd */
 typedef struct __call_single_data call_single_data_t
 	__aligned(sizeof(struct __call_single_data));
 
+/*
+ * Enqueue a llist_node on the call_single_queue; be very careful, read
+ * flush_smp_call_function_queue() in detail.
+ */
+extern void __smp_call_single_queue(int cpu, struct llist_node *node);
+
 /* total number of cpus in this system (may exceed NR_CPUS) */
 extern unsigned int total_cpus;
 

include/linux/swait.h

@@ -9,23 +9,10 @@
 #include <asm/current.h>
 
 /*
- * BROKEN wait-queues.
- *
- * These "simple" wait-queues are broken garbage, and should never be
- * used. The comments below claim that they are "similar" to regular
- * wait-queues, but the semantics are actually completely different, and
- * every single user we have ever had has been buggy (or pointless).
- *
- * A "swake_up_one()" only wakes up _one_ waiter, which is not at all what
- * "wake_up()" does, and has led to problems. In other cases, it has
- * been fine, because there's only ever one waiter (kvm), but in that
- * case gthe whole "simple" wait-queue is just pointless to begin with,
- * since there is no "queue". Use "wake_up_process()" with a direct
- * pointer instead.
- *
- * While these are very similar to regular wait queues (wait.h) the most
- * important difference is that the simple waitqueue allows for deterministic
- * behaviour -- IOW it has strictly bounded IRQ and lock hold times.
+ * Simple waitqueues are semantically very different to regular wait queues
+ * (wait.h). The most important difference is that the simple waitqueue allows
+ * for deterministic behaviour -- IOW it has strictly bounded IRQ and lock hold
+ * times.
  *
  * Mainly, this is accomplished by two things. Firstly not allowing swake_up_all
  * from IRQ disabled, and dropping the lock upon every wakeup, giving a higher
@@ -39,7 +26,7 @@
  *    sleeper state.
  *
  *  - the !exclusive mode; because that leads to O(n) wakeups, everything is
- *    exclusive.
+ *    exclusive. As such swake_up_one will only ever awake _one_ waiter.
  *
  *  - custom wake callback functions; because you cannot give any guarantees
  *    about random code. This also allows swait to be used in RT, such that