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 RFC tip/core/rcu 09/18] rcu: remove redundant grace-period check
Date: Tue, 15 Dec 2009 15:02:32 -0800 [thread overview]
Message-ID: <1260918161762-git-send-email-> (raw)
In-Reply-To: <20091215230213.GA9093@linux.vnet.ibm.com>
From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Proposed for 2.6.34, not for inclusion.
The rcu_process_dyntick() function checks twice for the end of
the current grace period. However, it holds the current rcu_node
structure's ->lock field throughout, and doesn't get to the second call
to rcu_gp_in_progress() unless there is at least one CPU corresponding
to this rcu_node structure that has not yet checked in for the current
grace period, which would prevent the current grace period from ending.
So the current grace period cannot have ended, and the second check is
redundant, so remove it.
Also, given that this function is used even with !CONFIG_NO_HZ, its name
is quite misleading. Change from rcu_process_dyntick() to force_qs_rnp().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 9 ++++-----
1 files changed, 4 insertions(+), 5 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 6268f37..d920285 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1146,8 +1146,7 @@ void rcu_check_callbacks(int cpu, int user)
* have not yet encountered a quiescent state, using the function specified.
* The caller must have suppressed start of new grace periods.
*/
-static void rcu_process_dyntick(struct rcu_state *rsp,
- int (*f)(struct rcu_data *))
+static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
{
unsigned long bit;
int cpu;
@@ -1172,7 +1171,7 @@ static void rcu_process_dyntick(struct rcu_state *rsp,
if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
mask |= bit;
}
- if (mask != 0 && rcu_gp_in_progress(rsp)) {
+ if (mask != 0) {
/* rcu_report_qs_rnp() releases rnp->lock. */
rcu_report_qs_rnp(mask, rsp, rnp, flags);
@@ -1222,7 +1221,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
break; /* So gcc recognizes the dead code. */
/* Record dyntick-idle state. */
- rcu_process_dyntick(rsp, dyntick_save_progress_counter);
+ force_qs_rnp(rsp, dyntick_save_progress_counter);
spin_lock(&rnp->lock); /* irqs already disabled */
if (rcu_gp_in_progress(rsp))
rsp->signaled = RCU_FORCE_QS;
@@ -1232,7 +1231,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
/* Check dyntick-idle state, send IPI to laggarts. */
spin_unlock(&rnp->lock); /* irqs remain disabled */
- rcu_process_dyntick(rsp, rcu_implicit_dynticks_qs);
+ force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
/* Leave state in case more forcing is required. */
--
1.5.2.5
next prev parent reply other threads:[~2009-12-15 23:11 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-12-15 23:02 [PATCH RFC tip/core/rcu 0/18] rcu: simplify race conditions, add checking Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 01/18] rcu: adjust force_quiescent_state() locking, step 1 Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 02/18] rcu: adjust force_quiescent_state() locking, step 2 Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 03/18] rcu: prohibit starting new grace periods while forcing quiescent states Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 04/18] rcu: eliminate local variable signaled from force_quiescent_state() Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 05/18] rcu: eliminate local variable lastcomp " Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 06/18] rcu: eliminate second argument of rcu_process_dyntick() Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 07/18] rcu: eliminate rcu_process_dyntick() return value Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 08/18] rcu: remove leg of force_quiescent_state() switch statement Paul E. McKenney
2009-12-15 23:02 ` Paul E. McKenney [this message]
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 10/18] rcu: make force_quiescent_state() start grace period if needed Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 11/18] rcu: add force_quiescent_state() testing to rcutorture Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 12/18] rcu: make MAINTAINERS file match new RCU reality Paul E. McKenney
2009-12-16 0:53 ` Josh Triplett
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 13/18] rcu: add debug check for too many rcu_read_unlock() Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 14/18] rcu: lockdep check for exiting to user space as RCU reader Paul E. McKenney
2009-12-16 10:24 ` Peter Zijlstra
2009-12-16 15:11 ` Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 15/18] rcu: give different levels of the rcu_node hierarchy distinct lockdep names Paul E. McKenney
2009-12-16 0:59 ` Josh Triplett
2009-12-16 1:59 ` Paul E. McKenney
2009-12-16 10:26 ` Peter Zijlstra
2009-12-16 10:33 ` Peter Zijlstra
2009-12-16 15:13 ` Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 16/18] rcu: make lockdep aware of SRCU read-side critical sections Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 17/18] rcu: Provide different lockdep classes for each flavor of RCU Paul E. McKenney
2009-12-15 23:02 ` [PATCH RFC tip/core/rcu 18/18] rcu: add primitives to check for RCU read-side critical sections Paul E. McKenney
2009-12-16 1:04 ` Josh Triplett
2009-12-16 2:08 ` Paul E. McKenney
2009-12-16 10:31 ` Peter Zijlstra
2009-12-16 15:18 ` Paul E. McKenney
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