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    Subject[PATCH 08/41] nohz: Try not to give the timekeeping duty to an adaptive tickless cpu
    Date
    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.

    [TODO: We need to find a way to ensure there is always one non-nohz
    running CPU maintaining the timekeeping duty if every non-idle CPUs are
    adaptive tickless]

    Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Alessio Igor Bogani <abogani@kernel.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Avi Kivity <avi@redhat.com>
    Cc: Chris Metcalf <cmetcalf@tilera.com>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
    Cc: Geoff Levand <geoff@infradead.org>
    Cc: Gilad Ben Yossef <gilad@benyossef.com>
    Cc: Hakan Akkan <hakanakkan@gmail.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Kevin Hilman <khilman@ti.com>
    Cc: Max Krasnyansky <maxk@qualcomm.com>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Stephen Hemminger <shemminger@vyatta.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    ---
    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 0695e9d..f1142d5 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>

    @@ -782,6 +783,45 @@ 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
    */
    @@ -798,17 +838,7 @@ 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


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