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Date: Tue, 17 Jan 2017 18:45:26 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
bobby.prani@...il.com,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH v2 tip/core/rcu 4/6] rcu: Abstract extended quiescent state determination
This commit is the fourth step towards full abstraction of all accesses
to the ->dynticks counter, implementing previously open-coded checks and
comparisons in new rcu_dynticks_in_eqs() and rcu_dynticks_in_eqs_since()
functions. This abstraction will ease changes to the ->dynticks counter
operation.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@...htriplett.org>
---
include/linux/rcutiny.h | 6 ++++++
kernel/rcu/tree.c | 52 +++++++++++++++++++++++++++++++++++-------------
kernel/rcu/tree.h | 2 ++
kernel/rcu/tree_exp.h | 6 +++---
kernel/rcu/tree_plugin.h | 2 +-
kernel/rcu/tree_trace.c | 2 +-
6 files changed, 51 insertions(+), 19 deletions(-)
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index ac81e4063b40..4f9b2fa2173d 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -27,6 +27,12 @@
#include <linux/cache.h>
+struct rcu_dynticks;
+static inline int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
+{
+ return 0;
+}
+
static inline unsigned long get_state_synchronize_rcu(void)
{
return 0;
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 70b01e1983e6..c5362b6c7ed3 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -337,10 +337,22 @@ static void rcu_dynticks_eqs_online(void)
}
/*
+ * Is the current CPU in an extended quiescent state?
+ *
+ * No ordering, as we are sampling CPU-local information.
+ */
+bool rcu_dynticks_curr_cpu_in_eqs(void)
+{
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+
+ return !(atomic_read(&rdtp->dynticks) & 0x1);
+}
+
+/*
* Snapshot the ->dynticks counter with full ordering so as to allow
* stable comparison of this counter with past and future snapshots.
*/
-static int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
+int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
{
int snap = atomic_add_return(0, &rdtp->dynticks);
@@ -348,6 +360,25 @@ static int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
}
/*
+ * Return true if the snapshot returned from rcu_dynticks_snap()
+ * indicates that RCU is in an extended quiescent state.
+ */
+static bool rcu_dynticks_in_eqs(int snap)
+{
+ return !(snap & 0x1);
+}
+
+/*
+ * Return true if the CPU corresponding to the specified rcu_dynticks
+ * structure has spent some time in an extended quiescent state since
+ * rcu_dynticks_snap() returned the specified snapshot.
+ */
+static bool rcu_dynticks_in_eqs_since(struct rcu_dynticks *rdtp, int snap)
+{
+ return snap != rcu_dynticks_snap(rdtp);
+}
+
+/*
* Do a double-increment of the ->dynticks counter to emulate a
* momentary idle-CPU quiescent state.
*/
@@ -1045,7 +1076,7 @@ void rcu_nmi_enter(void)
* to be in the outermost NMI handler that interrupted an RCU-idle
* period (observation due to Andy Lutomirski).
*/
- if (!(atomic_read(&rdtp->dynticks) & 0x1)) {
+ if (rcu_dynticks_curr_cpu_in_eqs()) {
rcu_dynticks_eqs_exit();
incby = 1;
}
@@ -1071,7 +1102,7 @@ void rcu_nmi_exit(void)
* to us!)
*/
WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
- WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+ WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());
/*
* If the nesting level is not 1, the CPU wasn't RCU-idle, so
@@ -1097,9 +1128,7 @@ void rcu_nmi_exit(void)
*/
bool notrace __rcu_is_watching(void)
{
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-
- return atomic_read(&rdtp->dynticks) & 0x1;
+ return !rcu_dynticks_curr_cpu_in_eqs();
}
/**
@@ -1184,7 +1213,7 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp,
{
rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks);
rcu_sysidle_check_cpu(rdp, isidle, maxj);
- if ((rdp->dynticks_snap & 0x1) == 0) {
+ if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4,
rdp->mynode->gpnum))
@@ -1203,12 +1232,7 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp,
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
bool *isidle, unsigned long *maxj)
{
- unsigned int curr;
int *rcrmp;
- unsigned int snap;
-
- curr = (unsigned int)rcu_dynticks_snap(rdp->dynticks);
- snap = (unsigned int)rdp->dynticks_snap;
/*
* If the CPU passed through or entered a dynticks idle phase with
@@ -1218,7 +1242,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
* read-side critical section that started before the beginning
* of the current RCU grace period.
*/
- if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
+ if (rcu_dynticks_in_eqs_since(rdp->dynticks, rdp->dynticks_snap)) {
trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
rdp->dynticks_fqs++;
return 1;
@@ -3807,7 +3831,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
- WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
+ WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));
rdp->cpu = cpu;
rdp->rsp = rsp;
rcu_boot_init_nocb_percpu_data(rdp);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index fe98dd24adf8..3b953dcf6afc 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -595,6 +595,8 @@ extern struct rcu_state rcu_bh_state;
extern struct rcu_state rcu_preempt_state;
#endif /* #ifdef CONFIG_PREEMPT_RCU */
+int rcu_dynticks_snap(struct rcu_dynticks *rdtp);
+
#ifdef CONFIG_RCU_BOOST
DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
DECLARE_PER_CPU(int, rcu_cpu_kthread_cpu);
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 011f626b2fd8..e155a465cf84 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -360,7 +360,7 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
rdp->exp_dynticks_snap =
rcu_dynticks_snap(rdp->dynticks);
if (raw_smp_processor_id() == cpu ||
- !(rdp->exp_dynticks_snap & 0x1) ||
+ rcu_dynticks_in_eqs(rdp->exp_dynticks_snap) ||
!(rnp->qsmaskinitnext & rdp->grpmask))
mask_ofl_test |= rdp->grpmask;
}
@@ -383,8 +383,8 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
if (!(mask_ofl_ipi & mask))
continue;
retry_ipi:
- if (rcu_dynticks_snap(rdp->dynticks) !=
- rdp->exp_dynticks_snap) {
+ if (rcu_dynticks_in_eqs_since(rdp->dynticks,
+ rdp->exp_dynticks_snap)) {
mask_ofl_test |= mask;
continue;
}
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 56583e764ebf..652209589adf 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1643,7 +1643,7 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
"o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
"N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
ticks_value, ticks_title,
- atomic_read(&rdtp->dynticks) & 0xfff,
+ rcu_dynticks_snap(rdtp) & 0xfff,
rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index b1f28972872c..b833cd0a29e8 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -124,7 +124,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
rdp->rcu_qs_ctr_snap == per_cpu(rcu_qs_ctr, rdp->cpu),
rdp->core_needs_qs);
seq_printf(m, " dt=%d/%llx/%d df=%lu",
- atomic_read(&rdp->dynticks->dynticks),
+ rcu_dynticks_snap(rdp->dynticks),
rdp->dynticks->dynticks_nesting,
rdp->dynticks->dynticks_nmi_nesting,
rdp->dynticks_fqs);
--
2.5.2
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