From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
peterz@infradead.org, rostedt@goodmis.org,
Valdis.Kletnieks@vt.edu, dhowells@redhat.com,
eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com,
sbw@mit.edu, patches@linaro.org,
"Paul E. McKenney" <paul.mckenney@linaro.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 21/23] rcu: Simplify quiescent-state detection
Date: Thu, 20 Sep 2012 11:48:17 -0700 [thread overview]
Message-ID: <1348166900-18716-21-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <1348166900-18716-1-git-send-email-paulmck@linux.vnet.ibm.com>
From: "Paul E. McKenney" <paul.mckenney@linaro.org>
The current quiescent-state detection algorithm is needlessly
complex. It records the grace-period number corresponding to
the quiescent state at the time of the quiescent state, which
works, but it seems better to simply erase any record of previous
quiescent states at the time that the CPU notices the new grace
period. This has the further advantage of removing another piece
of RCU for which lockless reasoning is required.
Therefore, this commit makes this change.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
kernel/rcutree.c | 27 +++++++++++----------------
kernel/rcutree.h | 2 --
kernel/rcutree_plugin.h | 2 --
kernel/rcutree_trace.c | 12 +++++-------
4 files changed, 16 insertions(+), 27 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 71ae31b..7a91dd4 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -176,8 +176,6 @@ void rcu_sched_qs(int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
- rdp->passed_quiesce_gpnum = rdp->gpnum;
- barrier();
if (rdp->passed_quiesce == 0)
trace_rcu_grace_period("rcu_sched", rdp->gpnum, "cpuqs");
rdp->passed_quiesce = 1;
@@ -187,8 +185,6 @@ void rcu_bh_qs(int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
- rdp->passed_quiesce_gpnum = rdp->gpnum;
- barrier();
if (rdp->passed_quiesce == 0)
trace_rcu_grace_period("rcu_bh", rdp->gpnum, "cpuqs");
rdp->passed_quiesce = 1;
@@ -897,12 +893,8 @@ static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct
*/
rdp->gpnum = rnp->gpnum;
trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpustart");
- if (rnp->qsmask & rdp->grpmask) {
- rdp->qs_pending = 1;
- rdp->passed_quiesce = 0;
- } else {
- rdp->qs_pending = 0;
- }
+ rdp->passed_quiesce = 0;
+ rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
zero_cpu_stall_ticks(rdp);
}
}
@@ -982,10 +974,13 @@ __rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat
* our behalf. Catch up with this state to avoid noting
* spurious new grace periods. If another grace period
* has started, then rnp->gpnum will have advanced, so
- * we will detect this later on.
+ * we will detect this later on. Of course, any quiescent
+ * states we found for the old GP are now invalid.
*/
- if (ULONG_CMP_LT(rdp->gpnum, rdp->completed))
+ if (ULONG_CMP_LT(rdp->gpnum, rdp->completed)) {
rdp->gpnum = rdp->completed;
+ rdp->passed_quiesce = 0;
+ }
/*
* If RCU does not need a quiescent state from this CPU,
@@ -1356,7 +1351,7 @@ rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
* based on quiescent states detected in an earlier grace period!
*/
static void
-rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastgp)
+rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
unsigned long mask;
@@ -1364,7 +1359,8 @@ rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long las
rnp = rdp->mynode;
raw_spin_lock_irqsave(&rnp->lock, flags);
- if (lastgp != rnp->gpnum || rnp->completed == rnp->gpnum) {
+ if (rdp->passed_quiesce == 0 || rdp->gpnum != rnp->gpnum ||
+ rnp->completed == rnp->gpnum) {
/*
* The grace period in which this quiescent state was
@@ -1423,7 +1419,7 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
* Tell RCU we are done (but rcu_report_qs_rdp() will be the
* judge of that).
*/
- rcu_report_qs_rdp(rdp->cpu, rsp, rdp, rdp->passed_quiesce_gpnum);
+ rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
}
#ifdef CONFIG_HOTPLUG_CPU
@@ -2598,7 +2594,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
rdp->completed = rnp->completed;
rdp->passed_quiesce = 0;
rdp->qs_pending = 0;
- rdp->passed_quiesce_gpnum = rnp->gpnum - 1;
trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuonl");
}
raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 8f0293c..935dd4c 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -246,8 +246,6 @@ struct rcu_data {
/* in order to detect GP end. */
unsigned long gpnum; /* Highest gp number that this CPU */
/* is aware of having started. */
- unsigned long passed_quiesce_gpnum;
- /* gpnum at time of quiescent state. */
bool passed_quiesce; /* User-mode/idle loop etc. */
bool qs_pending; /* Core waits for quiesc state. */
bool beenonline; /* CPU online at least once. */
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index b4e8eb2..4734afb 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -137,8 +137,6 @@ static void rcu_preempt_qs(int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
- rdp->passed_quiesce_gpnum = rdp->gpnum;
- barrier();
if (rdp->passed_quiesce == 0)
trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs");
rdp->passed_quiesce = 1;
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index f54f0ce..bd4df13 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -86,12 +86,11 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
{
if (!rdp->beenonline)
return;
- seq_printf(m, "%3d%cc=%lu g=%lu pq=%d pgp=%lu qp=%d",
+ seq_printf(m, "%3d%cc=%lu g=%lu pq=%d qp=%d",
rdp->cpu,
cpu_is_offline(rdp->cpu) ? '!' : ' ',
rdp->completed, rdp->gpnum,
- rdp->passed_quiesce, rdp->passed_quiesce_gpnum,
- rdp->qs_pending);
+ rdp->passed_quiesce, rdp->qs_pending);
seq_printf(m, " dt=%d/%llx/%d df=%lu",
atomic_read(&rdp->dynticks->dynticks),
rdp->dynticks->dynticks_nesting,
@@ -150,12 +149,11 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
{
if (!rdp->beenonline)
return;
- seq_printf(m, "%d,%s,%lu,%lu,%d,%lu,%d",
+ seq_printf(m, "%d,%s,%lu,%lu,%d,%d",
rdp->cpu,
cpu_is_offline(rdp->cpu) ? "\"N\"" : "\"Y\"",
rdp->completed, rdp->gpnum,
- rdp->passed_quiesce, rdp->passed_quiesce_gpnum,
- rdp->qs_pending);
+ rdp->passed_quiesce, rdp->qs_pending);
seq_printf(m, ",%d,%llx,%d,%lu",
atomic_read(&rdp->dynticks->dynticks),
rdp->dynticks->dynticks_nesting,
@@ -186,7 +184,7 @@ static int show_rcudata_csv(struct seq_file *m, void *unused)
int cpu;
struct rcu_state *rsp;
- seq_puts(m, "\"CPU\",\"Online?\",\"c\",\"g\",\"pq\",\"pgp\",\"pq\",");
+ seq_puts(m, "\"CPU\",\"Online?\",\"c\",\"g\",\"pq\",\"pq\",");
seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\",");
seq_puts(m, "\"of\",\"qll\",\"ql\",\"qs\"");
#ifdef CONFIG_RCU_BOOST
--
1.7.8
next prev parent reply other threads:[~2012-09-20 18:49 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-20 18:47 [PATCH tip/core/rcu 0/23] v2 Improvements to RT response on big systems and expedited functions Paul E. McKenney
2012-09-20 18:47 ` [PATCH tip/core/rcu 01/23] rcu: Move RCU grace-period initialization into a kthread Paul E. McKenney
2012-09-20 18:47 ` [PATCH tip/core/rcu 02/23] rcu: Prevent initialization-time quiescent-state race Paul E. McKenney
2012-09-20 18:47 ` [PATCH tip/core/rcu 03/23] rcu: Allow RCU grace-period initialization to be preempted Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 04/23] rcu: Move RCU grace-period cleanup into kthread Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 05/23] rcu: Allow RCU grace-period cleanup to be preempted Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 06/23] rcu: Break up rcu_gp_kthread() into subfunctions Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 07/23] rcu: Prevent offline CPUs from executing RCU core code Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 08/23] rcu: Provide OOM handler to motivate lazy RCU callbacks Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 09/23] rcu: Segregate rcu_state fields to improve cache locality Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 10/23] rcu: Move quiescent-state forcing into kthread Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 11/23] rcu: Allow RCU quiescent-state forcing to be preempted Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 12/23] rcu: Adjust debugfs tracing for kthread-based quiescent-state forcing Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 13/23] rcu: Prevent force_quiescent_state() memory contention Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 14/23] rcu: Control grace-period duration from sysfs Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 15/23] rcu: Make rcutree module parameters visible in sysfs Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 16/23] rcu: Fix day-zero grace-period initialization/cleanup race Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 17/23] rcu: Add random PROVE_RCU_DELAY to grace-period initialization Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 18/23] rcu: Adjust for unconditional ->completed assignment Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 19/23] rcu: Eliminate signed overflow in synchronize_rcu_expedited() Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 20/23] rcu: Reduce synchronize_rcu_expedited() latency Paul E. McKenney
2012-09-20 18:48 ` Paul E. McKenney [this message]
2012-09-20 18:48 ` [PATCH tip/core/rcu 22/23] rcu: Handle unbalanced rcu_node configurations with few CPUs Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 23/23] rcu: Shrink RCU based on number of CPUs Paul E. McKenney
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