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rcu: Eliminate local variable lastcomp from force_quiescent_state() 

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>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12626465502985-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul E. McKenney 2010-01-04 15:09:04 -08:00 committed by Ingo Molnar
parent f3a8b5c6aa
commit 39c0bbfc07
2 changed files with 3 additions and 9 deletions
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10
kernel/rcutree.c
View File

@ -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. */

2
kernel/rcutree.h
View File

@ -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 */