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Date: Mon, 20 Dec 2010 16:24:12 +0100 From: Frederic Weisbecker <fweisbec@...il.com> To: LKML <linux-kernel@...r.kernel.org> Cc: LKML <linux-kernel@...r.kernel.org>, Frederic Weisbecker <fweisbec@...il.com>, Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>, Lai Jiangshan <laijs@...fujitsu.com>, Andrew Morton <akpm@...ux-foundation.org>, Anton Blanchard <anton@....ibm.com>, Tim Pepper <lnxninja@...ux.vnet.ibm.com> Subject: [RFC PATCH 05/15] nohz_task: Restart the tick when another task compete on the cpu If a new task is enqueued on the same cpu than a nohz task, then the tick must be restarted in case it was stopped for the nohz task, so that preemption can work again. Do this remotely using a specific IPI. Signed-off-by: Frederic Weisbecker <fweisbec@...il.com> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> Cc: Ingo Molnar <mingo@...e.hu> Cc: Steven Rostedt <rostedt@...dmis.org> Cc: Lai Jiangshan <laijs@...fujitsu.com> Cc: Andrew Morton <akpm@...ux-foundation.org> Cc: Anton Blanchard <anton@....ibm.com> Cc: Tim Pepper <lnxninja@...ux.vnet.ibm.com> --- include/linux/sched.h | 2 ++ kernel/sched.c | 45 ++++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 46 insertions(+), 1 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 858a876..f80088a 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2550,8 +2550,10 @@ extern void task_oncpu_function_call(struct task_struct *p, void (*func) (void *info), void *info); #ifdef CONFIG_NO_HZ_TASK +extern void smp_send_update_nohz_task_cpu(int cpu); extern int nohz_task_can_stop_tick(void); #else +static inline void smp_send_update_nohz_task_cpu(int cpu) { } static inline int nohz_task_can_stop_tick(void) { return 0; } #endif diff --git a/kernel/sched.c b/kernel/sched.c index e9cdd7a..6dbae46 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2446,6 +2446,27 @@ static void update_avg(u64 *avg, u64 sample) #ifdef CONFIG_NO_HZ_TASK DEFINE_PER_CPU(int, task_nohz_mode); +/* Must be called with irq disabled! */ +static void nohz_task_cpu_update(void *unused) +{ + struct rq *rq; + int cpu; + + if (!__get_cpu_var(task_nohz_mode)) + return; + + /* + * Look at nr_running lockless. At worst, the new task was deactivated + * and we just exit without doing anything. + */ + rq = this_rq(); + cpu = smp_processor_id(); + if (rq->nr_running > 1) { + __get_cpu_var(task_nohz_mode) = 0; + tick_nohz_restart_sched_tick(); + } +} + int nohz_task_can_stop_tick(void) { struct rq *rq = this_rq(); @@ -2455,6 +2476,12 @@ int nohz_task_can_stop_tick(void) return 1; } + +void smp_send_update_nohz_task_cpu(int cpu) +{ + smp_call_function_single(cpu, nohz_task_cpu_update, + NULL, 0); +} #endif static inline void ttwu_activate(struct task_struct *p, struct rq *rq, @@ -2477,6 +2504,8 @@ static inline void ttwu_activate(struct task_struct *p, struct rq *rq, static inline void ttwu_post_activation(struct task_struct *p, struct rq *rq, int wake_flags, bool success) { + int cpu = cpu_of(rq); + trace_sched_wakeup(p, success); check_preempt_curr(rq, p, wake_flags); @@ -2498,7 +2527,21 @@ static inline void ttwu_post_activation(struct task_struct *p, struct rq *rq, #endif /* if a worker is waking up, notify workqueue */ if ((p->flags & PF_WQ_WORKER) && success) - wq_worker_waking_up(p, cpu_of(rq)); + wq_worker_waking_up(p, cpu); + +#ifdef CONFIG_NO_HZ_TASK + /* + * CHECKME: + * Ideally, we need to check if the target has a nohz task + * and only send the IPI if so. But there is nothing but + * a racy way to do that. Or can we assume at that point + * of the wake up that if cpu_has_nohz_task(cpu) is 0, then + * it's ok, even if it has a task about to switch to nohz + * task mode? + */ + if (rq->nr_running == 2) + smp_send_update_nohz_task_cpu(cpu); +#endif } /** -- 1.7.3.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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