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    Subject[PATCH v13 18/18] sched: use static key for sched_clock_running
    Date
    sched_clock_running may be read every time sched_clock_cpu() is called.
    Yet, this variable is updated only twice during boot, and never changes
    again, therefore it is better to make it a static key.

    Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
    ---
    kernel/sched/clock.c | 16 ++++++++--------
    kernel/sched/debug.c | 2 --
    2 files changed, 8 insertions(+), 10 deletions(-)

    diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
    index 4d07b785d566..07e54073d6af 100644
    --- a/kernel/sched/clock.c
    +++ b/kernel/sched/clock.c
    @@ -66,7 +66,7 @@ unsigned long long __weak sched_clock(void)
    }
    EXPORT_SYMBOL_GPL(sched_clock);

    -__read_mostly int sched_clock_running;
    +static DEFINE_STATIC_KEY_FALSE(sched_clock_running);

    #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
    /*
    @@ -190,7 +190,7 @@ void clear_sched_clock_stable(void)

    smp_mb(); /* matches sched_clock_init_late() */

    - if (sched_clock_running == 2)
    + if (static_key_count(&sched_clock_running.key) == 2)
    __clear_sched_clock_stable();
    }

    @@ -203,7 +203,7 @@ void __init sched_clock_init(void)
    {
    unsigned long flags;

    - sched_clock_running = 1;
    + static_branch_inc(&sched_clock_running);

    /* Adjust __gtod_offset for contigious transition from early clock */
    local_irq_save(flags);
    @@ -217,7 +217,7 @@ void __init sched_clock_init(void)
    */
    static int __init sched_clock_init_late(void)
    {
    - sched_clock_running = 2;
    + static_branch_inc(&sched_clock_running);
    /*
    * Ensure that it is impossible to not do a static_key update.
    *
    @@ -362,7 +362,7 @@ u64 sched_clock_cpu(int cpu)
    if (sched_clock_stable())
    return sched_clock() + __sched_clock_offset;

    - if (unlikely(!sched_clock_running))
    + if (!static_branch_unlikely(&sched_clock_running))
    return sched_clock();

    preempt_disable_notrace();
    @@ -385,7 +385,7 @@ void sched_clock_tick(void)
    if (sched_clock_stable())
    return;

    - if (unlikely(!sched_clock_running))
    + if (!static_branch_unlikely(&sched_clock_running))
    return;

    lockdep_assert_irqs_disabled();
    @@ -444,13 +444,13 @@ EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);

    void __init sched_clock_init(void)
    {
    - sched_clock_running = 1;
    + static_branch_inc(&sched_clock_running);
    generic_sched_clock_init();
    }

    u64 sched_clock_cpu(int cpu)
    {
    - if (unlikely(!sched_clock_running))
    + if (!static_branch_unlikely(&sched_clock_running))
    return 0;

    return sched_clock();
    diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
    index e593b4118578..b0212f489a33 100644
    --- a/kernel/sched/debug.c
    +++ b/kernel/sched/debug.c
    @@ -623,8 +623,6 @@ void print_dl_rq(struct seq_file *m, int cpu, struct dl_rq *dl_rq)
    #undef PU
    }

    -extern __read_mostly int sched_clock_running;
    -
    static void print_cpu(struct seq_file *m, int cpu)
    {
    struct rq *rq = cpu_rq(cpu);
    --
    2.18.0
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