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Message-Id: <1367599676-2049-3-git-send-email-fweisbec@gmail.com>
Date: Fri, 3 May 2013 18:47:56 +0200
From: Frederic Weisbecker <fweisbec@...il.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Christoph Lameter <cl@...ux.com>,
Hakan Akkan <hakanakkan@...il.com>,
Kevin Hilman <khilman@...aro.org>,
Li Zhong <zhong@...ux.vnet.ibm.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Paul Gortmaker <paul.gortmaker@...driver.com>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 2/2] sched: Keep at least 1 tick per second for active dynticks tasks
The scheduler doesn't yet fully support environments
with a single task running without a periodic tick.
In order to ensure we still maintain the duties of scheduler_tick(),
keep at least 1 tick per second.
This makes sure that we keep the progression of various scheduler
accounting and background maintainance even with a very low granularity.
Examples include cpu load, sched average, CFS entity vruntime,
avenrun and events such as load balancing, amongst other details
handled in sched_class::task_tick().
This limitation will be removed in the future once we get
these individual items to work in full dynticks CPUs.
Suggested-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Hakan Akkan <hakanakkan@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Kevin Hilman <khilman@...aro.org>
Cc: Li Zhong <zhong@...ux.vnet.ibm.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
include/linux/sched.h | 1 +
kernel/sched/core.c | 30 ++++++++++++++++++++++++++++++
kernel/sched/idle_task.c | 1 +
kernel/sched/sched.h | 10 ++++++++++
kernel/time/tick-sched.c | 7 +++++++
5 files changed, 49 insertions(+), 0 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ebf7095..af008d7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1862,6 +1862,7 @@ static inline void wake_up_nohz_cpu(int cpu) { }
#ifdef CONFIG_NO_HZ_FULL
extern bool sched_can_stop_tick(void);
+extern u64 scheduler_tick_max_deferment(void);
#else
static inline bool sched_can_stop_tick(void) { return false; }
#endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e94842d..3bdf986 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2736,8 +2736,35 @@ void scheduler_tick(void)
rq->idle_balance = idle_cpu(cpu);
trigger_load_balance(rq, cpu);
#endif
+ rq_last_tick_reset(rq);
}
+#ifdef CONFIG_NO_HZ_FULL
+/**
+ * scheduler_tick_max_deferment
+ *
+ * Keep at least one tick per second when a single
+ * active task is running because the scheduler doesn't
+ * yet completely support full dynticks environment.
+ *
+ * This makes sure that uptime, CFS vruntime, load
+ * balancing, etc... continue to move forward, even
+ * with a very low granularity.
+ */
+u64 scheduler_tick_max_deferment(void)
+{
+ struct rq *rq = this_rq();
+ unsigned long next, now = ACCESS_ONCE(jiffies);
+
+ next = rq->last_sched_tick + HZ;
+
+ if (time_before_eq(next, now))
+ return 0;
+
+ return jiffies_to_usecs(next - now) * NSEC_PER_USEC;
+}
+#endif
+
notrace unsigned long get_parent_ip(unsigned long addr)
{
if (in_lock_functions(addr)) {
@@ -6993,6 +7020,9 @@ void __init sched_init(void)
#ifdef CONFIG_NO_HZ_COMMON
rq->nohz_flags = 0;
#endif
+#ifdef CONFIG_NO_HZ_FULL
+ rq->last_sched_tick = 0;
+#endif
#endif
init_rq_hrtick(rq);
atomic_set(&rq->nr_iowait, 0);
diff --git a/kernel/sched/idle_task.c b/kernel/sched/idle_task.c
index b8ce773..d8da010 100644
--- a/kernel/sched/idle_task.c
+++ b/kernel/sched/idle_task.c
@@ -17,6 +17,7 @@ select_task_rq_idle(struct task_struct *p, int sd_flag, int flags)
static void pre_schedule_idle(struct rq *rq, struct task_struct *prev)
{
idle_exit_fair(rq);
+ rq_last_tick_reset(rq);
}
static void post_schedule_idle(struct rq *rq)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 24dc298..ce39224 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -410,6 +410,9 @@ struct rq {
u64 nohz_stamp;
unsigned long nohz_flags;
#endif
+#ifdef CONFIG_NO_HZ_FULL
+ unsigned long last_sched_tick;
+#endif
int skip_clock_update;
/* capture load from *all* tasks on this cpu: */
@@ -1090,6 +1093,13 @@ static inline void dec_nr_running(struct rq *rq)
rq->nr_running--;
}
+static inline void rq_last_tick_reset(struct rq *rq)
+{
+#ifdef CONFIG_NO_HZ_FULL
+ rq->last_sched_tick = jiffies;
+#endif
+}
+
extern void update_rq_clock(struct rq *rq);
extern void activate_task(struct rq *rq, struct task_struct *p, int flags);
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 1c9f53b..07929c6 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -600,6 +600,13 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
time_delta = KTIME_MAX;
}
+#ifdef CONFIG_NO_HZ_FULL
+ if (!ts->inidle) {
+ time_delta = min(time_delta,
+ scheduler_tick_max_deferment());
+ }
+#endif
+
/*
* calculate the expiry time for the next timer wheel
* timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
--
1.7.5.4
--
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