Commit-ID: d3052109c0bc9e536d17d627ae628ed8ceb6928c
Gitweb: https://git.kernel.org/tip/d3052109c0bc9e536d17d627ae628ed8ceb6928c
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Wed, 25 Jul 2018 11:49:47 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Thu, 30 Aug 2018 16:03:44 -0700
rcu: More aggressively enlist scheduler aid for nohz_full CPUs
Because nohz_full CPUs can leave the scheduler-clock interrupt disabled
even when in kernel mode, RCU cannot rely on rcu_check_callbacks() to
enlist the scheduler's aid in extracting a quiescent state from such CPUs.
This commit therefore more aggressively uses resched_cpu() on nohz_full
CPUs that fail to pass through a quiescent state in a timely manner.
By default, the resched_cpu() beating starts 300 milliseconds into the
quiescent state.
While in the neighborhood, add a ->last_fqs_resched field to the rcu_data
structure in order to rate-limit resched_cpu() calls from the RCU
grace-period kthread.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcu/tree.c | 32 ++++++++++++++++++++++++++------
kernel/rcu/tree.h | 1 +
kernel/rcu/tree_plugin.h | 1 +
3 files changed, 28 insertions(+), 6 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 6bd0951a5f3a..96731f62594a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -61,6 +61,7 @@
#include <linux/trace_events.h>
#include <linux/suspend.h>
#include <linux/ftrace.h>
+#include <linux/tick.h>
#include "tree.h"
#include "rcu.h"
@@ -1088,19 +1089,38 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
WRITE_ONCE(*rnhqp, true);
/* Store rcu_need_heavy_qs before rcu_urgent_qs. */
smp_store_release(ruqp, true);
- rcu_state.jiffies_resched += jtsq; /* Re-enable beating. */
} else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
WRITE_ONCE(*ruqp, true);
}
/*
- * If more than halfway to RCU CPU stall-warning time, do a
- * resched_cpu() to try to loosen things up a bit. Also check to
- * see if the CPU is getting hammered with interrupts, but only
- * once per grace period, just to keep the IPIs down to a dull roar.
+ * NO_HZ_FULL CPUs can run in-kernel without rcu_check_callbacks!
+ * The above code handles this, but only for straight cond_resched().
+ * And some in-kernel loops check need_resched() before calling
+ * cond_resched(), which defeats the above code for CPUs that are
+ * running in-kernel with scheduling-clock interrupts disabled.
+ * So hit them over the head with the resched_cpu() hammer!
*/
- if (time_after(jiffies, rcu_state.jiffies_resched)) {
+ if (tick_nohz_full_cpu(rdp->cpu) &&
+ time_after(jiffies,
+ READ_ONCE(rdp->last_fqs_resched) + jtsq * 3)) {
resched_cpu(rdp->cpu);
+ WRITE_ONCE(rdp->last_fqs_resched, jiffies);
+ }
+
+ /*
+ * If more than halfway to RCU CPU stall-warning time, invoke
+ * resched_cpu() more frequently to try to loosen things up a bit.
+ * Also check to see if the CPU is getting hammered with interrupts,
+ * but only once per grace period, just to keep the IPIs down to
+ * a dull roar.
+ */
+ if (time_after(jiffies, rcu_state.jiffies_resched)) {
+ if (time_after(jiffies,
+ READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
+ resched_cpu(rdp->cpu);
+ WRITE_ONCE(rdp->last_fqs_resched, jiffies);
+ }
if (IS_ENABLED(CONFIG_IRQ_WORK) &&
!rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
(rnp->ffmask & rdp->grpmask)) {
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 4866fa44ab0b..8f053bb1eec8 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -260,6 +260,7 @@ struct rcu_data {
short rcu_ofl_gp_flags; /* ->gp_flags at last offline. */
unsigned long rcu_onl_gp_seq; /* ->gp_seq at last online. */
short rcu_onl_gp_flags; /* ->gp_flags at last online. */
+ unsigned long last_fqs_resched; /* Time of last rcu_resched(). */
int cpu;
};
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 7ec366268e2e..1e80a0da7924 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1850,6 +1850,7 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
rdp->ticks_this_gp = 0;
rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
+ WRITE_ONCE(rdp->last_fqs_resched, jiffies);
}
#ifdef CONFIG_RCU_NOCB_CPU
|