lkml.org 
[lkml]   [2019]   [Oct]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip: core/rcu] rcu: Make CPU-hotplug removal operations enable tick
The following commit has been merged into the core/rcu branch of tip:

Commit-ID: 96926686deab853bcacf887501f4ed958e38666b
Gitweb: https://git.kernel.org/tip/96926686deab853bcacf887501f4ed958e38666b
Author: Paul E. McKenney <paulmck@kernel.org>
AuthorDate: Fri, 02 Aug 2019 15:12:47 -07:00
Committer: Paul E. McKenney <paulmck@kernel.org>
CommitterDate: Sat, 05 Oct 2019 10:46:05 -07:00

rcu: Make CPU-hotplug removal operations enable tick

CPU-hotplug removal operations run the multi_cpu_stop() function, which
relies on the scheduler to gain control from whatever is running on the
various online CPUs, including any nohz_full CPUs running long loops in
kernel-mode code. Lack of the scheduler-clock interrupt on such CPUs
can delay multi_cpu_stop() for several minutes and can also result in
RCU CPU stall warnings. This commit therefore causes CPU-hotplug removal
operations to enable the scheduler-clock interrupt on all online CPUs.

[ paulmck: Apply Joel Fernandes TICK_DEP_MASK_RCU->TICK_DEP_BIT_RCU fix. ]
[ paulmck: Apply simplifications suggested by Frederic Weisbecker. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index a5c296d..7c67ea5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2101,6 +2101,9 @@ int rcutree_dead_cpu(unsigned int cpu)
rcu_boost_kthread_setaffinity(rnp, -1);
/* Do any needed no-CB deferred wakeups from this CPU. */
do_nocb_deferred_wakeup(per_cpu_ptr(&rcu_data, cpu));
+
+ // Stop-machine done, so allow nohz_full to disable tick.
+ tick_dep_clear(TICK_DEP_BIT_RCU);
return 0;
}

@@ -3085,6 +3088,9 @@ int rcutree_online_cpu(unsigned int cpu)
return 0; /* Too early in boot for scheduler work. */
sync_sched_exp_online_cleanup(cpu);
rcutree_affinity_setting(cpu, -1);
+
+ // Stop-machine done, so allow nohz_full to disable tick.
+ tick_dep_clear(TICK_DEP_BIT_RCU);
return 0;
}

@@ -3105,6 +3111,9 @@ int rcutree_offline_cpu(unsigned int cpu)
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

rcutree_affinity_setting(cpu, cpu);
+
+ // nohz_full CPUs need the tick for stop-machine to work quickly
+ tick_dep_set(TICK_DEP_BIT_RCU);
return 0;
}

\
 
 \ /
  Last update: 2019-10-31 12:56    [W:0.043 / U:0.024 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site