From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752800AbaGHWzg (ORCPT ); Tue, 8 Jul 2014 18:55:36 -0400 Received: from mail-yh0-f51.google.com ([209.85.213.51]:64863 "EHLO mail-yh0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750947AbaGHWzf (ORCPT ); Tue, 8 Jul 2014 18:55:35 -0400 From: Pranith Kumar To: "Paul E. McKenney" , Josh Triplett , linux-kernel@vger.kernel.org (open list:READ-COPY UPDATE...) Subject: [RFC PATCH 1/1] rcu: use atomic_read(v) instead of atomic_add_return(0, v) Date: Tue, 8 Jul 2014 18:55:45 -0400 Message-Id: <1404860145-16450-1-git-send-email-bobby.prani@gmail.com> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org atomic_add_return() invalidates the cache line in other processors where-as atomic_read does not. I don't see why we would need invalidation in this case. If indeed it was need a comment would be helpful for readers. Otherwise doesn't using atomic_read() make more sense here? RFC! replace atomic_add_return(0, v) with atomic_read(v) as the latter is better. Signed-off-by: Pranith Kumar --- kernel/rcu/tree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index dac6d20..a4a8f5f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -891,7 +891,7 @@ static int rcu_is_cpu_rrupt_from_idle(void) static int dyntick_save_progress_counter(struct rcu_data *rdp, bool *isidle, unsigned long *maxj) { - rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks); + rdp->dynticks_snap = atomic_read(&rdp->dynticks->dynticks); rcu_sysidle_check_cpu(rdp, isidle, maxj); if ((rdp->dynticks_snap & 0x1) == 0) { trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti")); @@ -920,7 +920,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, int *rcrmp; unsigned int snap; - curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks); + curr = (unsigned int)atomic_read(&rdp->dynticks->dynticks); snap = (unsigned int)rdp->dynticks_snap; /* -- 1.9.1