Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934117AbcCOETt (ORCPT ); Tue, 15 Mar 2016 00:19:49 -0400 Received: from prod-mail-xrelay05.akamai.com ([23.79.238.179]:53369 "EHLO prod-mail-xrelay05.akamai.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932490AbcCOETr (ORCPT ); Tue, 15 Mar 2016 00:19:47 -0400 From: Joshua Hunt To: akpm@linux-foundation.org, uobergfe@redhat.com, dzickus@redhat.com Cc: linux-kernel@vger.kernel.org, Joshua Hunt Subject: [PATCH v2] watchdog: don't run proc_watchdog_update if new value is same as old Date: Tue, 15 Mar 2016 00:19:44 -0400 Message-Id: <1458015584-13814-1-git-send-email-johunt@akamai.com> X-Mailer: git-send-email 1.7.9.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1973 Lines: 59 While working on a script to restore all sysctl params before a series of tests I found that writing any value into the /proc/sys/kernel/{nmi_watchdog,soft_watchdog,watchdog,watchdog_thresh} causes them to call proc_watchdog_update(). [ 955.756196] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. [ 955.765994] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. [ 955.774619] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. [ 955.783182] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. There doesn't appear to be a reason for doing this work every time a write occurs, so only do it when the values change. Signed-off-by: Josh Hunt Cc: # 4.1.x- --- kernel/watchdog.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) v2: Update changelog to no longer include mention of soft lockup, and add stable. diff --git a/kernel/watchdog.c b/kernel/watchdog.c index b3ace6e..9acb29f 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -923,6 +923,9 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write, * both lockup detectors are disabled if proc_watchdog_update() * returns an error. */ + if (old == new) + goto out; + err = proc_watchdog_update(); } out: @@ -967,7 +970,7 @@ int proc_soft_watchdog(struct ctl_table *table, int write, int proc_watchdog_thresh(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos) { - int err, old; + int err, old, new; get_online_cpus(); mutex_lock(&watchdog_proc_mutex); @@ -987,6 +990,10 @@ int proc_watchdog_thresh(struct ctl_table *table, int write, /* * Update the sample period. Restore on failure. */ + new = ACCESS_ONCE(watchdog_thresh); + if (old == new) + goto out; + set_sample_period(); err = proc_watchdog_update(); if (err) { -- 1.7.9.5