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    Subject[PATCH 24/27] nohz: Add some tracing
    Date
    Not for merge, just for debugging.

    Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Alessio Igor Bogani <abogani@kernel.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Chris Metcalf <cmetcalf@tilera.com>
    Cc: Christoph Lameter <cl@linux.com>
    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: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    ---
    kernel/time/tick-sched.c | 27 ++++++++++++++++++++++-----
    1 files changed, 22 insertions(+), 5 deletions(-)

    diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
    index eb6ad3d..0e1ebff 100644
    --- a/kernel/time/tick-sched.c
    +++ b/kernel/time/tick-sched.c
    @@ -142,6 +142,7 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
    ts->idle_jiffies++;
    }
    #endif
    + trace_printk("tick\n");
    update_process_times(user_mode(regs));
    profile_tick(CPU_PROFILING);
    }
    @@ -591,17 +592,30 @@ void tick_nohz_idle_enter(void)
    #ifdef CONFIG_NO_HZ_FULL
    static bool can_stop_full_tick(int cpu)
    {
    - if (!sched_can_stop_tick())
    + if (!sched_can_stop_tick()) {
    + trace_printk("Can't stop: sched\n");
    return false;
    + }

    - if (!rcu_is_nocb_cpu(cpu))
    + if (!rcu_is_nocb_cpu(cpu)) {
    + trace_printk("Can't stop: not RCU nocb\n");
    return false;
    + }

    - if (rcu_pending(cpu))
    + /*
    + * Keep the tick if we are asked to report a quiescent state.
    + * This must be further optimized (avoid checks for local callbacks,
    + * ignore RCU in userspace, etc...
    + */
    + if (rcu_pending(cpu)) {
    + trace_printk("Can't stop: RCU pending\n");
    return false;
    + }

    - if (posix_cpu_timers_running(current))
    + if (posix_cpu_timers_running(current)) {
    + trace_printk("Can't stop: posix CPU timers running\n");
    return false;
    + }

    return true;
    }
    @@ -615,12 +629,15 @@ static void tick_nohz_full_stop_tick(struct tick_sched *ts)
    if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
    return;

    - if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
    + if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) {
    + trace_printk("Can't stop: NOHZ_MODE_INACTIVE\n");
    return;
    + }

    if (!can_stop_full_tick(cpu))
    return;

    + trace_printk("Stop tick\n");
    tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
    #endif
    }
    --
    1.7.5.4


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