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, dvhltc@us.ibm.com, niv@us.ibm.com,
tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org,
Valdis.Kletnieks@vt.edu, dhowells@redhat.com,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 4/4] rcu: simplify association of quiescent states with grace periods
Date: Tue, 10 Nov 2009 13:37:22 -0800 [thread overview]
Message-ID: <12578890421011-git-send-email-> (raw)
In-Reply-To: <20091110213651.GA21411@linux.vnet.ibm.com>
From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The rdp->passed_quiesc_completed fields are used to properly associate
the recorded quiescent state with a grace period. It is OK to wrongly
associate a given quiescent state with a preceding grace period, but it
is fatal to associate a given quiescent state with a grace period
that begins after the quiescent state occurred. Grace periods are
numbered, and the following fields track them:
o ->gpnum is the number of the grace period currently in progress,
or the number of the last grace period to complete if no grace
period is currently in progress.
o ->completed is the number of the last grace period to have
completed.
These two fields are equal if there is no grace period in progress,
otherwise ->gpnum is one greater than ->completed. But the
rdp->passed_quiesc_completed field compared against ->completed,
and if equal, the quiescent state is presumed to count against the
current grace period.
The earlier code copied rdp->completed to rdp->passed_quiesc_completed,
which has been made to work, but is error-prone. In contrast, copying
one less than rdp->gpnum is guaranteed safe, because rdp->gpnum is not
incremented until after the start of the corresponding grace period.
At the end of the grace period, when ->completed has incremented, then
any quiescent periods recorded previously will be discarded.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 4 ++--
kernel/rcutree_plugin.h | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 4026560..2f5d8c5 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -100,7 +100,7 @@ void rcu_sched_qs(int cpu)
struct rcu_data *rdp;
rdp = &per_cpu(rcu_sched_data, cpu);
- rdp->passed_quiesc_completed = rdp->completed;
+ rdp->passed_quiesc_completed = rdp->gpnum - 1;
barrier();
rdp->passed_quiesc = 1;
rcu_preempt_note_context_switch(cpu);
@@ -111,7 +111,7 @@ void rcu_bh_qs(int cpu)
struct rcu_data *rdp;
rdp = &per_cpu(rcu_bh_data, cpu);
- rdp->passed_quiesc_completed = rdp->completed;
+ rdp->passed_quiesc_completed = rdp->gpnum - 1;
barrier();
rdp->passed_quiesc = 1;
}
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 9744dfc..b7dc0c2 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -67,7 +67,7 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed);
static void rcu_preempt_qs(int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
- rdp->passed_quiesc_completed = rdp->completed;
+ rdp->passed_quiesc_completed = rdp->gpnum - 1;
barrier();
rdp->passed_quiesc = 1;
}
--
1.5.2.5
next prev parent reply other threads:[~2009-11-10 21:37 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-10 21:36 [PATCH tip/core/rcu 0/4] rcu inline, expedited, ->completed cleanups Paul E. McKenney
2009-11-10 21:37 ` [PATCH tip/core/rcu 1/4] rcu: remove inline from forward-referenced functions Paul E. McKenney
2009-11-10 22:27 ` [tip:core/rcu] rcu: Remove " tip-bot for Paul E. McKenney
2009-11-10 22:38 ` Joe Perches
2009-11-10 22:59 ` Paul E. McKenney
2009-11-10 23:06 ` Joe Perches
2009-11-10 23:41 ` Paul E. McKenney
2009-11-11 1:03 ` Joe Perches
2009-11-11 1:42 ` Paul E. McKenney
2009-11-11 3:28 ` Joe Perches
2009-11-11 4:50 ` Paul E. McKenney
2009-11-11 5:41 ` Paul E. McKenney
2009-11-11 7:02 ` Ingo Molnar
2009-11-11 19:47 ` Paul E. McKenney
2009-11-10 23:03 ` [PATCH tip/core/rcu 1/4] rcu: remove " Josh Triplett
2009-11-10 21:37 ` [PATCH tip/core/rcu 2/4] rcu: enable synchronize_sched_expedited() fastpath Paul E. McKenney
2009-11-10 22:27 ` [tip:core/rcu] rcu: Enable " tip-bot for Paul E. McKenney
2009-11-10 21:37 ` [PATCH tip/core/rcu 3/4] rcu: rename dynticks_completed to completed_fqs Paul E. McKenney
2009-11-10 22:28 ` [tip:core/rcu] rcu: Rename " tip-bot for Paul E. McKenney
2009-11-10 21:37 ` Paul E. McKenney [this message]
2009-11-10 22:28 ` [tip:core/rcu] rcu: Simplify association of quiescent states with grace periods tip-bot for Paul E. McKenney
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