Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765933Ab3DFQqV (ORCPT ); Sat, 6 Apr 2013 12:46:21 -0400 Received: from mail-wg0-f42.google.com ([74.125.82.42]:62165 "EHLO mail-wg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750890Ab3DFQqP (ORCPT ); Sat, 6 Apr 2013 12:46:15 -0400 From: Frederic Weisbecker To: Ingo Molnar Cc: LKML , Frederic Weisbecker , Alessio Igor Bogani , Andrew Morton , Chris Metcalf , Christoph Lameter , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , Li Zhong , Namhyung Kim , "Paul E. McKenney" , Paul Gortmaker , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Paul Turner , Mike Galbraith Subject: [PATCH 3/7] sched: Update rq clock on tickless CPUs before calling check_preempt_curr() Date: Sat, 6 Apr 2013 18:45:56 +0200 Message-Id: <1365266760-24725-4-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.7.5.4 In-Reply-To: <1365266760-24725-1-git-send-email-fweisbec@gmail.com> References: <1365266760-24725-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2533 Lines: 74 check_preempt_wakeup() of fair class needs an uptodate sched clock value to update runtime stats of the current task. When a task is woken up, activate_task() is usually called right before ttwu_do_wakeup() unless the task is still in the runqueue. In this case we need to update the rq clock manually in case the CPU runs tickless because ttwu_do_wakeup() calls check_preempt_wakeup(). Signed-off-by: Frederic Weisbecker Cc: Alessio Igor Bogani Cc: Andrew Morton Cc: Chris Metcalf Cc: Christoph Lameter Cc: Geoff Levand Cc: Gilad Ben Yossef Cc: Hakan Akkan Cc: Ingo Molnar Cc: Li Zhong Cc: Namhyung Kim Cc: Paul E. McKenney Cc: Paul Gortmaker Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Paul Turner Cc: Mike Galbraith --- kernel/sched/core.c | 17 ++++++++++++++++- 1 files changed, 16 insertions(+), 1 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 1826e00..e4ec9d5 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1352,6 +1352,12 @@ static int ttwu_remote(struct task_struct *p, int wake_flags) rq = __task_rq_lock(p); if (p->on_rq) { + /* + * Ensure check_preempt_curr() won't deal with a stale value + * of rq clock if the CPU is tickless. BTW do we actually need + * check_preempt_curr() to be called here? + */ + update_nohz_rq_clock(rq); ttwu_do_wakeup(rq, p, wake_flags); ret = 1; } @@ -1529,8 +1535,17 @@ static void try_to_wake_up_local(struct task_struct *p) if (!(p->state & TASK_NORMAL)) goto out; - if (!p->on_rq) + if (!p->on_rq) { ttwu_activate(rq, p, ENQUEUE_WAKEUP); + } else { + /* + * Even if the task is on the runqueue we still + * need to ensure check_preempt_curr() won't + * deal with a stale rq clock value on a tickless + * CPU + */ + update_nohz_rq_clock(rq); + } ttwu_do_wakeup(rq, p, 0); ttwu_stat(p, smp_processor_id(), 0); -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/