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    Subject[PATCH tip/core/rcu 06/14] rcu: Export RCU_FAST_NO_HZ parameters to sysfs
    Date
    From: "Paul E. McKenney" <paul.mckenney@linaro.org>

    RCU_FAST_NO_HZ operation is controlled by four compile-time C-preprocessor
    macros, but some use cases benefit greatly from runtime adjustment,
    particularly when tuning devices. This commit therefore creates the
    corresponding sysfs entries.

    Reported-by: Robin Randhawa <robin.randhawa@arm.com>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    kernel/rcutree_plugin.h | 31 ++++++++++++++++++++-----------
    1 files changed, 20 insertions(+), 11 deletions(-)

    diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
    index ab1bdde..0997e9f 100644
    --- a/kernel/rcutree_plugin.h
    +++ b/kernel/rcutree_plugin.h
    @@ -1617,6 +1617,15 @@ static void rcu_idle_count_callbacks_posted(void)
    #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
    #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */

    +static int rcu_idle_flushes = RCU_IDLE_FLUSHES;
    +module_param(rcu_idle_flushes, int, 0644);
    +static int rcu_idle_opt_flushes = RCU_IDLE_OPT_FLUSHES;
    +module_param(rcu_idle_opt_flushes, int, 0644);
    +static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
    +module_param(rcu_idle_gp_delay, int, 0644);
    +static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
    +module_param(rcu_idle_lazy_gp_delay, int, 0644);
    +
    extern int tick_nohz_enabled;

    /*
    @@ -1696,10 +1705,10 @@ int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
    }
    /* Set up for the possibility that RCU will post a timer. */
    if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
    - *delta_jiffies = round_up(RCU_IDLE_GP_DELAY + jiffies,
    - RCU_IDLE_GP_DELAY) - jiffies;
    + *delta_jiffies = round_up(rcu_idle_gp_delay + jiffies,
    + rcu_idle_gp_delay) - jiffies;
    } else {
    - *delta_jiffies = jiffies + RCU_IDLE_LAZY_GP_DELAY;
    + *delta_jiffies = jiffies + rcu_idle_lazy_gp_delay;
    *delta_jiffies = round_jiffies(*delta_jiffies) - jiffies;
    }
    return 0;
    @@ -1805,11 +1814,11 @@ static void rcu_prepare_for_idle(int cpu)
    if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
    trace_rcu_prep_idle("User dyntick with callbacks");
    rdtp->idle_gp_timer_expires =
    - round_up(jiffies + RCU_IDLE_GP_DELAY,
    - RCU_IDLE_GP_DELAY);
    + round_up(jiffies + rcu_idle_gp_delay,
    + rcu_idle_gp_delay);
    } else if (rcu_cpu_has_callbacks(cpu)) {
    rdtp->idle_gp_timer_expires =
    - round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
    + round_jiffies(jiffies + rcu_idle_lazy_gp_delay);
    trace_rcu_prep_idle("User dyntick with lazy callbacks");
    } else {
    return;
    @@ -1861,8 +1870,8 @@ static void rcu_prepare_for_idle(int cpu)
    /* Check and update the ->dyntick_drain sequencing. */
    if (rdtp->dyntick_drain <= 0) {
    /* First time through, initialize the counter. */
    - rdtp->dyntick_drain = RCU_IDLE_FLUSHES;
    - } else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES &&
    + rdtp->dyntick_drain = rcu_idle_flushes;
    + } else if (rdtp->dyntick_drain <= rcu_idle_opt_flushes &&
    !rcu_pending(cpu) &&
    !local_softirq_pending()) {
    /* Can we go dyntick-idle despite still having callbacks? */
    @@ -1871,11 +1880,11 @@ static void rcu_prepare_for_idle(int cpu)
    if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
    trace_rcu_prep_idle("Dyntick with callbacks");
    rdtp->idle_gp_timer_expires =
    - round_up(jiffies + RCU_IDLE_GP_DELAY,
    - RCU_IDLE_GP_DELAY);
    + round_up(jiffies + rcu_idle_gp_delay,
    + rcu_idle_gp_delay);
    } else {
    rdtp->idle_gp_timer_expires =
    - round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
    + round_jiffies(jiffies + rcu_idle_lazy_gp_delay);
    trace_rcu_prep_idle("Dyntick with lazy callbacks");
    }
    tp = &rdtp->idle_gp_timer;
    --
    1.7.8


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