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 05/18] rcu: eliminate local variable lastcomp from force_quiescent_state()
Date: Tue, 15 Dec 2009 15:02:28 -0800 [thread overview]
Message-ID: <12609181612745-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.
Because rsp->fqs_active is set to 1 across force_quiescent_state()'s
switch statement, rcu_start_gp() will refrain from starting a new
grace period during this time. Therefore, rsp->gpnum is constant,
and can be propagated to all uses of lastcomp, eliminating this local
variable.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 10 +++-------
kernel/rcutree.h | 2 --
2 files changed, 3 insertions(+), 9 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 1d8cfb1..62b6433 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1191,7 +1191,6 @@ static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
{
unsigned long flags;
- long lastcomp;
struct rcu_node *rnp = rcu_get_root(rsp);
u8 forcenow;
u8 gpdone;
@@ -1207,7 +1206,6 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
goto unlock_fqs_ret; /* no emergency and done recently. */
rsp->n_force_qs++;
spin_lock(&rnp->lock); /* irqs already disabled */
- lastcomp = rsp->gpnum - 1;
rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
if(!rcu_gp_in_progress(rsp)) {
rsp->n_force_qs_ngp++;
@@ -1228,7 +1226,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
break; /* So gcc recognizes the dead code. */
/* Record dyntick-idle state. */
- gpdone = rcu_process_dyntick(rsp, lastcomp,
+ gpdone = rcu_process_dyntick(rsp, rsp->gpnum - 1,
dyntick_save_progress_counter);
spin_lock(&rnp->lock); /* irqs already disabled */
if (gpdone)
@@ -1239,11 +1237,9 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
/* Update state, record completion counter. */
forcenow = 0;
- if (lastcomp + 1 == rsp->gpnum &&
- lastcomp == rsp->completed) {
+ if (rsp->gpnum - 1 == rsp->completed) {
forcenow = rsp->signaled == RCU_SAVE_COMPLETED;
rsp->signaled = RCU_FORCE_QS;
- rsp->completed_fqs = lastcomp;
}
if (!forcenow)
break;
@@ -1253,7 +1249,7 @@ 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 */
- gpdone = rcu_process_dyntick(rsp, rsp->completed_fqs,
+ gpdone = rcu_process_dyntick(rsp, rsp->gpnum - 1,
rcu_implicit_dynticks_qs);
/* Leave state in case more forcing is required. */
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index dc386a7..5348561 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -296,8 +296,6 @@ struct rcu_state {
long orphan_qlen; /* Number of orphaned cbs. */
spinlock_t fqslock; /* Only one task forcing */
/* quiescent states. */
- long completed_fqs; /* Value of completed @ snap. */
- /* Protected by fqslock. */
unsigned long jiffies_force_qs; /* Time at which to invoke */
/* force_quiescent_state(). */
unsigned long n_force_qs; /* Number of calls to */
--
1.5.2.5
next prev parent reply other threads:[~2009-12-15 23:03 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 ` Paul E. McKenney [this message]
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 ` [PATCH RFC tip/core/rcu 09/18] rcu: remove redundant grace-period check Paul E. McKenney
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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