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Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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Pull RCU updates from Ingo Molnar:
 "This cycle's RCU changes were:

   - A few more RCU flavor consolidation cleanups.

   - Updates to RCU's list-traversal macros improving lockdep usability.

   - Forward-progress improvements for no-CBs CPUs: Avoid ignoring
     incoming callbacks during grace-period waits.

   - Forward-progress improvements for no-CBs CPUs: Use ->cblist
     structure to take advantage of others' grace periods.

   - Also added a small commit that avoids needlessly inflicting
     scheduler-clock ticks on callback-offloaded CPUs.

   - Forward-progress improvements for no-CBs CPUs: Reduce contention on
     ->nocb_lock guarding ->cblist.

   - Forward-progress improvements for no-CBs CPUs: Add ->nocb_bypass
     list to further reduce contention on ->nocb_lock guarding ->cblist.

   - Miscellaneous fixes.

   - Torture-test updates.

   - minor LKMM updates"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (86 commits)
  MAINTAINERS: Update from paulmck@linux.ibm.com to paulmck@kernel.org
  rcu: Don't include <linux/ktime.h> in rcutiny.h
  rcu: Allow rcu_do_batch() to dynamically adjust batch sizes
  rcu/nocb: Don't wake no-CBs GP kthread if timer posted under overload
  rcu/nocb: Reduce __call_rcu_nocb_wake() leaf rcu_node ->lock contention
  rcu/nocb: Reduce nocb_cb_wait() leaf rcu_node ->lock contention
  rcu/nocb: Advance CBs after merge in rcutree_migrate_callbacks()
  rcu/nocb: Avoid synchronous wakeup in __call_rcu_nocb_wake()
  rcu/nocb: Print no-CBs diagnostics when rcutorture writer unduly delayed
  rcu/nocb: EXP Check use and usefulness of ->nocb_lock_contended
  rcu/nocb: Add bypass callback queueing
  rcu/nocb: Atomic ->len field in rcu_segcblist structure
  rcu/nocb: Unconditionally advance and wake for excessive CBs
  rcu/nocb: Reduce ->nocb_lock contention with separate ->nocb_gp_lock
  rcu/nocb: Reduce contention at no-CBs invocation-done time
  rcu/nocb: Reduce contention at no-CBs registry-time CB advancement
  rcu/nocb: Round down for number of no-CBs grace-period kthreads
  rcu/nocb: Avoid ->nocb_lock capture by corresponding CPU
  rcu/nocb: Avoid needless wakeups of no-CBs grace-period kthread
  rcu/nocb: Make __call_rcu_nocb_wake() safe for many callbacks
  ...
This commit is contained in:
Linus Torvalds
2019-09-16 16:28:19 -07:00
parent d75a43c645 4a0fa886ab
commit 94d18ee934
49 changed files with 1499 additions and 805 deletions
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57
kernel/sched/core.c
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@@ -3486,8 +3486,36 @@ void scheduler_tick(void)
struct tick_work {
int cpu;
atomic_t state;
struct delayed_work work;
};
/* Values for ->state, see diagram below. */
#define TICK_SCHED_REMOTE_OFFLINE 0
#define TICK_SCHED_REMOTE_OFFLINING 1
#define TICK_SCHED_REMOTE_RUNNING 2
/*
* State diagram for ->state:
*
*
* TICK_SCHED_REMOTE_OFFLINE
* | ^
* | |
* | | sched_tick_remote()
* | |
* | |
* +--TICK_SCHED_REMOTE_OFFLINING
* | ^
* | |
* sched_tick_start() | | sched_tick_stop()
* | |
* V |
* TICK_SCHED_REMOTE_RUNNING
*
*
* Other transitions get WARN_ON_ONCE(), except that sched_tick_remote()
* and sched_tick_start() are happy to leave the state in RUNNING.
*/
static struct tick_work __percpu *tick_work_cpu;
@@ -3500,6 +3528,7 @@ static void sched_tick_remote(struct work_struct *work)
struct task_struct *curr;
struct rq_flags rf;
u64 delta;
int os;
/*
* Handle the tick only if it appears the remote CPU is running in full
@@ -3513,7 +3542,7 @@ static void sched_tick_remote(struct work_struct *work)
rq_lock_irq(rq, &rf);
curr = rq->curr;
if (is_idle_task(curr))
if (is_idle_task(curr) || cpu_is_offline(cpu))
goto out_unlock;
update_rq_clock(rq);
@@ -3533,13 +3562,18 @@ out_requeue:
/*
* Run the remote tick once per second (1Hz). This arbitrary
* frequency is large enough to avoid overload but short enough
* to keep scheduler internal stats reasonably up to date.
* to keep scheduler internal stats reasonably up to date. But
* first update state to reflect hotplug activity if required.
*/
queue_delayed_work(system_unbound_wq, dwork, HZ);
os = atomic_fetch_add_unless(&twork->state, -1, TICK_SCHED_REMOTE_RUNNING);
WARN_ON_ONCE(os == TICK_SCHED_REMOTE_OFFLINE);
if (os == TICK_SCHED_REMOTE_RUNNING)
queue_delayed_work(system_unbound_wq, dwork, HZ);
}
static void sched_tick_start(int cpu)
{
int os;
struct tick_work *twork;
if (housekeeping_cpu(cpu, HK_FLAG_TICK))
@@ -3548,15 +3582,20 @@ static void sched_tick_start(int cpu)
WARN_ON_ONCE(!tick_work_cpu);
twork = per_cpu_ptr(tick_work_cpu, cpu);
twork->cpu = cpu;
INIT_DELAYED_WORK(&twork->work, sched_tick_remote);
queue_delayed_work(system_unbound_wq, &twork->work, HZ);
os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_RUNNING);
WARN_ON_ONCE(os == TICK_SCHED_REMOTE_RUNNING);
if (os == TICK_SCHED_REMOTE_OFFLINE) {
twork->cpu = cpu;
INIT_DELAYED_WORK(&twork->work, sched_tick_remote);
queue_delayed_work(system_unbound_wq, &twork->work, HZ);
}
}
#ifdef CONFIG_HOTPLUG_CPU
static void sched_tick_stop(int cpu)
{
struct tick_work *twork;
int os;
if (housekeeping_cpu(cpu, HK_FLAG_TICK))
return;
@@ -3564,7 +3603,10 @@ static void sched_tick_stop(int cpu)
WARN_ON_ONCE(!tick_work_cpu);
twork = per_cpu_ptr(tick_work_cpu, cpu);
cancel_delayed_work_sync(&twork->work);
/* There cannot be competing actions, but don't rely on stop-machine. */
os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_OFFLINING);
WARN_ON_ONCE(os != TICK_SCHED_REMOTE_RUNNING);
/* Don't cancel, as this would mess up the state machine. */
}
#endif /* CONFIG_HOTPLUG_CPU */
@@ -3572,7 +3614,6 @@ int __init sched_tick_offload_init(void)
{
tick_work_cpu = alloc_percpu(struct tick_work);
BUG_ON(!tick_work_cpu);
return 0;
}