linux-kernel - [PATCH tip/core/rcu 18/21] rcu: The rcu_gp_cleanup() function does not need cpu_needs_another

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Message-Id: <1524452624-27589-18-git-send-email-paulmck@linux.vnet.ibm.com>
Date:   Sun, 22 Apr 2018 20:03:41 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel.opensrc@...il.com,
        torvalds@...ux-foundation.org, npiggin@...il.com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 18/21] rcu: The rcu_gp_cleanup() function does not need cpu_needs_another_gp()

All of the cpu_needs_another_gp() function's checks (except for
newly arrived callbacks) have been subsumed into the rcu_gp_cleanup()
function's scan of the rcu_node tree.  This commit therefore drops the
call to cpu_needs_another_gp().  The check for newly arrived callbacks
is supplied by rcu_accelerate_cbs().  Any needed advancing (as in the
earlier rcu_advance_cbs() call) will be supplied when the corresponding
CPU becomes aware of the end of the now-completed grace period.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 07bccb1f0c87..7776d709e060 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2150,11 +2150,9 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
 		needgp = true;
 	}
 	/* Advance CBs to reduce false positives below. */
-	needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
-	if (needgp || cpu_needs_another_gp(rsp, rdp)) {
+	if (!rcu_accelerate_cbs(rsp, rnp, rdp) && needgp) {
 		WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
-		trace_rcu_grace_period(rsp->name,
-				       READ_ONCE(rsp->gpnum),
+		trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
 				       TPS("newreq"));
 	}
 	WRITE_ONCE(rsp->gp_flags, rsp->gp_flags & RCU_GP_FLAG_INIT);
-- 
2.5.2