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Subject[PATCH tip/core/rcu 05/11] rcu: eliminate local variable lastcomp from force_quiescent_state()
Date
From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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


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