rcu: Remove leg of force_quiescent_state() switch statement
Paul E. McKenney [Mon, 4 Jan 2010 23:09:07 +0000 (15:09 -0800)]
The comparisons of rsp->gpnum nad rsp->completed in
rcu_process_dyntick() and force_quiescent_state() can be
replaced by the much more clear rcu_gp_in_progress() predicate
function.  After doing this, it becomes clear that the
RCU_SAVE_COMPLETED leg of the force_quiescent_state() function's
switch statement is almost completely a no-op.  A small change
to the RCU_SAVE_DYNTICK leg renders it a complete no-op, after
which it can be removed.  Doing so also eliminates the forcenow
local variable from force_quiescent_state().

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: <12626465501781-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/rcutree.c
kernel/rcutree.h

index e497119..6268f37 100644 (file)
@@ -1144,6 +1144,7 @@ void rcu_check_callbacks(int cpu, int user)
 /*
  * Scan the leaf rcu_node structures, processing dyntick state for any that
  * 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 *))
@@ -1157,7 +1158,7 @@ static void rcu_process_dyntick(struct rcu_state *rsp,
        rcu_for_each_leaf_node(rsp, rnp) {
                mask = 0;
                spin_lock_irqsave(&rnp->lock, flags);
-               if (rnp->completed != rsp->gpnum - 1) {
+               if (!rcu_gp_in_progress(rsp)) {
                        spin_unlock_irqrestore(&rnp->lock, flags);
                        return;
                }
@@ -1171,7 +1172,7 @@ static void rcu_process_dyntick(struct rcu_state *rsp,
                        if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
                                mask |= bit;
                }
-               if (mask != 0 && rnp->completed == rsp->gpnum - 1) {
+               if (mask != 0 && rcu_gp_in_progress(rsp)) {
 
                        /* rcu_report_qs_rnp() releases rnp->lock. */
                        rcu_report_qs_rnp(mask, rsp, rnp, flags);
@@ -1189,7 +1190,6 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 {
        unsigned long flags;
        struct rcu_node *rnp = rcu_get_root(rsp);
-       u8 forcenow;
 
        if (!rcu_gp_in_progress(rsp))
                return;  /* No grace period in progress, nothing to force. */
@@ -1224,21 +1224,9 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
                /* Record dyntick-idle state. */
                rcu_process_dyntick(rsp, dyntick_save_progress_counter);
                spin_lock(&rnp->lock);  /* irqs already disabled */
-               if (!rcu_gp_in_progress(rsp))
-                       break;
-               /* fall into next case. */
-
-       case RCU_SAVE_COMPLETED:
-
-               /* Update state, record completion counter. */
-               forcenow = 0;
-               if (rsp->gpnum - 1 == rsp->completed) {
-                       forcenow = rsp->signaled == RCU_SAVE_COMPLETED;
+               if (rcu_gp_in_progress(rsp))
                        rsp->signaled = RCU_FORCE_QS;
-               }
-               if (!forcenow)
-                       break;
-               /* fall into next case. */
+               break;
 
        case RCU_FORCE_QS:
 
index 5348561..edb6fae 100644 (file)
@@ -237,12 +237,11 @@ struct rcu_data {
 #define RCU_GP_IDLE            0       /* No grace period in progress. */
 #define RCU_GP_INIT            1       /* Grace period being initialized. */
 #define RCU_SAVE_DYNTICK       2       /* Need to scan dyntick state. */
-#define RCU_SAVE_COMPLETED     3       /* Need to save rsp->completed. */
-#define RCU_FORCE_QS           4       /* Need to force quiescent state. */
+#define RCU_FORCE_QS           3       /* Need to force quiescent state. */
 #ifdef CONFIG_NO_HZ
 #define RCU_SIGNAL_INIT                RCU_SAVE_DYNTICK
 #else /* #ifdef CONFIG_NO_HZ */
-#define RCU_SIGNAL_INIT                RCU_SAVE_COMPLETED
+#define RCU_SIGNAL_INIT                RCU_FORCE_QS
 #endif /* #else #ifdef CONFIG_NO_HZ */
 
 #define RCU_JIFFIES_TILL_FORCE_QS       3      /* for rsp->jiffies_force_qs */