From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752109Ab2LTSeK (ORCPT ); Thu, 20 Dec 2012 13:34:10 -0500 Received: from mail-wg0-f43.google.com ([74.125.82.43]:58577 "EHLO mail-wg0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751744Ab2LTSdk (ORCPT ); Thu, 20 Dec 2012 13:33:40 -0500 From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Alessio Igor Bogani , Andrew Morton , Avi Kivity , Chris Metcalf , Christoph Lameter , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , Ingo Molnar , "Paul E. McKenney" , Paul Gortmaker , Peter Zijlstra , Steven Rostedt , Thomas Gleixner Subject: [PATCH 07/24] nohz: Assign timekeeping duty to a non-full-nohz CPU Date: Thu, 20 Dec 2012 19:32:54 +0100 Message-Id: <1356028391-14427-8-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.7.5.4 In-Reply-To: <1356028391-14427-1-git-send-email-fweisbec@gmail.com> References: <1356028391-14427-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This way the full nohz CPUs can safely run with the tick stopped with a guarantee that somebody else is taking care of the jiffies and gtod progression. NOTE: this doesn't handle CPU hotplug. Also we could use something more elaborated wrt. powersaving if we have more than one non full-nohz CPU running. But let's use this KISS solution for now. Signed-off-by: Frederic Weisbecker Cc: Alessio Igor Bogani Cc: Andrew Morton Cc: Avi Kivity Cc: Chris Metcalf Cc: Christoph Lameter Cc: Geoff Levand Cc: Gilad Ben Yossef Cc: Hakan Akkan Cc: Ingo Molnar Cc: Paul E. McKenney Cc: Paul Gortmaker Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner --- kernel/time/tick-broadcast.c | 3 ++- kernel/time/tick-common.c | 5 ++++- kernel/time/tick-sched.c | 7 ++++++- 3 files changed, 12 insertions(+), 3 deletions(-) diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c index f113755..596c547 100644 --- a/kernel/time/tick-broadcast.c +++ b/kernel/time/tick-broadcast.c @@ -537,7 +537,8 @@ void tick_broadcast_setup_oneshot(struct clock_event_device *bc) bc->event_handler = tick_handle_oneshot_broadcast; /* Take the do_timer update */ - tick_do_timer_cpu = cpu; + if (!tick_nohz_full_cpu(cpu)) + tick_do_timer_cpu = cpu; /* * We must be careful here. There might be other CPUs diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index b1600a6..83f2bd9 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -163,7 +163,10 @@ static void tick_setup_device(struct tick_device *td, * this cpu: */ if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) { - tick_do_timer_cpu = cpu; + if (!tick_nohz_full_cpu(cpu)) + tick_do_timer_cpu = cpu; + else + tick_do_timer_cpu = TICK_DO_TIMER_NONE; tick_next_period = ktime_get(); tick_period = ktime_set(0, NSEC_PER_SEC / HZ); } diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index fac9ba4..4a68b50 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -112,7 +112,8 @@ static void tick_sched_do_timer(ktime_t now) * this duty, then the jiffies update is still serialized by * jiffies_lock. */ - if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) + if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE) + && !tick_nohz_full_cpu(cpu)) tick_do_timer_cpu = cpu; #endif @@ -512,6 +513,10 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) return false; } + /* If there are full nohz CPUs around, we need to keep the timekeeping duty */ + if (have_full_nohz_mask && tick_do_timer_cpu == cpu) + return false; + return true; } -- 1.7.5.4