lkml.org 
[lkml]   [2010]   [Jan]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip:core/rcu] rcu: Remove leg of force_quiescent_state() switch statement
Commit-ID:  ee47eb9f4da6f44af965d6d049e77ee8c8a4b822
Gitweb: http://git.kernel.org/tip/ee47eb9f4da6f44af965d6d049e77ee8c8a4b822
Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Mon, 4 Jan 2010 15:09:07 -0800
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 13 Jan 2010 09:06:04 +0100

rcu: Remove leg of force_quiescent_state() switch statement

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 | 22 +++++-----------------
kernel/rcutree.h | 5 ++---
2 files changed, 7 insertions(+), 20 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index e497119..6268f37 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -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:

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 5348561..edb6fae 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -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 */

\
 
 \ /
  Last update: 2010-01-13 11:29    [from the cache]
©2003-2011 Jasper Spaans