[PATCH 12/32] nohz: Try not to give the timekeeping duty to a cpuset nohz cpu

Frederic Weisbecker
2011-08-15T15:53:24Z

Try to give the timekeeing duty to a CPU that doesn't belong
to any nohz cpuset when possible, so that we increase the chance
for these nohz cpusets to run their CPUs out of periodic tick
mode.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Anton Blanchard <anton@au1.ibm.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Pepper <lnxninja@linux.vnet.ibm.com>
---
kernel/time/tick-sched.c | 52 ++++++++++++++++++++++++++++++++++++---------
1 files changed, 41 insertions(+), 11 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index f5e12da..5f41ef7 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -20,6 +20,7 @@
#include <linux/profile.h>
#include <linux/sched.h>
#include <linux/module.h>
+#include <linux/cpuset.h>

#include <asm/irq_regs.h>

@@ -729,6 +730,45 @@ void tick_check_idle(int cpu)
tick_check_nohz(cpu);
}

+#ifdef CONFIG_CPUSETS_NO_HZ
+
+/*
+ * Take the timer duty if nobody is taking care of it.
+ * If a CPU already does and and it's in a nohz cpuset,
+ * then take the charge so that it can switch to nohz mode.
+ */
+static void tick_do_timer_check_handler(int cpu)
+{
+ int handler = tick_do_timer_cpu;
+
+ if (unlikely(handler == TICK_DO_TIMER_NONE)) {
+ tick_do_timer_cpu = cpu;
+ } else {
+ if (!cpuset_adaptive_nohz() &&
+ cpuset_cpu_adaptive_nohz(handler))
+ tick_do_timer_cpu = cpu;
+ }
+}
+
+#else
+
+static void tick_do_timer_check_handler(int cpu)
+{
+#ifdef CONFIG_NO_HZ
+ /*
+ * Check if the do_timer duty was dropped. We don't care about
+ * concurrency: This happens only when the cpu in charge went
+ * into a long sleep. If two cpus happen to assign themself to
+ * this duty, then the jiffies update is still serialized by
+ * xtime_lock.
+ */
+ if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
+ tick_do_timer_cpu = cpu;
+#endif
+}
+
+#endif /* CONFIG_CPUSETS_NO_HZ */
+
/*
* High resolution timer specific code
*/
@@ -745,17 +785,7 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
ktime_t now = ktime_get();
int cpu = smp_processor_id();

-#ifdef CONFIG_NO_HZ
- /*
- * Check if the do_timer duty was dropped. We don't care about
- * concurrency: This happens only when the cpu in charge went
- * into a long sleep. If two cpus happen to assign themself to
- * this duty, then the jiffies update is still serialized by
- * xtime_lock.
- */
- if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
- tick_do_timer_cpu = cpu;
-#endif
+ tick_do_timer_check_handler(cpu);

/* Check, if the jiffies need an update */
if (tick_do_timer_cpu == cpu)
--
1.7.5.4