linux-kernel - [RFC v2 14/18] rcu: Store first_gp_fqs into struct rcu

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Date:	Mon, 21 Sep 2015 15:03:55 +0200
From:	Petr Mladek <pmladek@...e.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...e.de>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	Vlastimil Babka <vbabka@...e.cz>,
	live-patching@...r.kernel.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>
Subject: [RFC v2 14/18] rcu: Store first_gp_fqs into struct rcu_state

We are going to try split the rcu kthread into few kthread works.
We will not stay in the funciton all the time and "first_gp_fqs"
variable will not preserve the state. Let's store it into
struct rcu_state.

Note that this change is needed only when the split into more
kthread works is accepted.

The patch does not change the existing behavior.

Signed-off-by: Petr Mladek <pmladek@...e.com>
---
 kernel/rcu/tree.c | 11 +++++------
 kernel/rcu/tree.h |  2 ++
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 5413d87a67c6..5a3e70a21df8 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1927,7 +1927,7 @@ static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
 /*
  * Do one round of quiescent-state forcing.
  */
-static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
+static void rcu_gp_fqs(struct rcu_state *rsp)
 {
 	bool isidle = false;
 	unsigned long maxj;
@@ -1935,7 +1935,7 @@ static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
 
 	WRITE_ONCE(rsp->gp_activity, jiffies);
 	rsp->n_force_qs++;
-	if (first_time) {
+	if (rsp->first_gp_fqs) {
 		/* Collect dyntick-idle snapshots. */
 		if (is_sysidle_rcu_state(rsp)) {
 			isidle = true;
@@ -1944,6 +1944,7 @@ static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
 		force_qs_rnp(rsp, dyntick_save_progress_counter,
 			     &isidle, &maxj);
 		rcu_sysidle_report_gp(rsp, isidle, maxj);
+		rsp->first_gp_fqs = false;
 	} else {
 		/* Handle dyntick-idle and offline CPUs. */
 		isidle = true;
@@ -2038,7 +2039,6 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
  */
 static int __noreturn rcu_gp_kthread(void *arg)
 {
-	bool first_gp_fqs;
 	int gf;
 	unsigned long j;
 	int ret;
@@ -2070,7 +2070,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
 		}
 
 		/* Handle quiescent-state forcing. */
-		first_gp_fqs = true;
+		rsp->first_gp_fqs = true;
 		j = jiffies_till_first_fqs;
 		if (j > HZ) {
 			j = HZ;
@@ -2098,8 +2098,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
 				trace_rcu_grace_period(rsp->name,
 						       READ_ONCE(rsp->gpnum),
 						       TPS("fqsstart"));
-				rcu_gp_fqs(rsp, first_gp_fqs);
-				first_gp_fqs = false;
+				rcu_gp_fqs(rsp);
 				trace_rcu_grace_period(rsp->name,
 						       READ_ONCE(rsp->gpnum),
 						       TPS("fqsend"));
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index de370b611837..f16578a5eefe 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -470,6 +470,8 @@ struct rcu_state {
 	wait_queue_head_t gp_wq;		/* Where GP task waits. */
 	short gp_flags;				/* Commands for GP task. */
 	short gp_state;				/* GP kthread sleep state. */
+	bool first_gp_fqs;			/* Do we force QS for */
+						/* the first time? */
 
 	/* End of fields guarded by root rcu_node's lock. */
 
-- 
1.8.5.6

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