rcu: Eliminate local variable lastcomp from force_quiescent_state()
Paul E. McKenney [Mon, 4 Jan 2010 23:09:04 +0000 (15:09 -0800)]
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>

kernel/rcutree.c
kernel/rcutree.h

index 1d8cfb1..62b6433 100644 (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. */
index dc386a7..5348561 100644 (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 */