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    SubjectRe: [PATCH] avoid using smp_processor_id() in preemptible code (nr_iowait_cpu)

    I've changed struct tick_sched to match passed *ts and cpu. Also changed "&per_cpu(tick_cpu_sched, cpu)"
    call to "struct tick_sched *tick_get_tick_sched(int cpu)" which we already have.

    But I don't really like this part:
    struct tick_sched *tick_get_tick_sched(int cpu)
    {
    struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    ts->cpu = cpu;
    ^^^^^^^^^^^^^
    return ts;
    }

    Please kindly review.

    ---

    diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
    index 52ff8aa..4871ed5 100644
    --- a/drivers/cpuidle/governors/menu.c
    +++ b/drivers/cpuidle/governors/menu.c
    @@ -137,14 +137,17 @@ static inline int which_bucket(unsigned int duration)
    {
    int bucket = 0;

    + int cpu = get_cpu();
    /*
    * We keep two groups of stats; one with no
    * IO pending, one without.
    * This allows us to calculate
    * E(duration)|iowait
    */
    - if (nr_iowait_cpu())
    + if (nr_iowait_cpu(cpu))
    bucket = BUCKETS/2;
    +
    + put_cpu();

    if (duration < 10)
    return bucket;
    @@ -169,14 +172,17 @@ static inline int which_bucket(unsigned int duration)
    static inline int performance_multiplier(void)
    {
    int mult = 1;
    -
    + int cpu = get_cpu();
    +
    /* for higher loadavg, we are more reluctant */

    mult += 2 * get_loadavg();

    /* for IO wait tasks (per cpu!) we add 5x each */
    - mult += 10 * nr_iowait_cpu();
    + mult += 10 * nr_iowait_cpu(cpu);

    + put_cpu();
    +
    return mult;
    }

    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index f118809..747fcae 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -139,7 +139,7 @@ extern int nr_processes(void);
    extern unsigned long nr_running(void);
    extern unsigned long nr_uninterruptible(void);
    extern unsigned long nr_iowait(void);
    -extern unsigned long nr_iowait_cpu(void);
    +extern unsigned long nr_iowait_cpu(int cpu);
    extern unsigned long this_cpu_load(void);


    diff --git a/include/linux/tick.h b/include/linux/tick.h
    index b232ccc..db14691 100644
    --- a/include/linux/tick.h
    +++ b/include/linux/tick.h
    @@ -51,6 +51,7 @@ struct tick_sched {
    unsigned long check_clocks;
    enum tick_nohz_mode nohz_mode;
    ktime_t idle_tick;
    + int cpu;
    int inidle;
    int tick_stopped;
    unsigned long idle_jiffies;
    diff --git a/kernel/sched.c b/kernel/sched.c
    index f8b8996..f61b48e 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -2864,9 +2864,9 @@ unsigned long nr_iowait(void)
    return sum;
    }

    -unsigned long nr_iowait_cpu(void)
    +unsigned long nr_iowait_cpu(int cpu)
    {
    - struct rq *this = this_rq();
    + struct rq *this = cpu_rq(cpu);
    return atomic_read(&this->nr_iowait);
    }

    diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
    index 1d7b9bc..5105345 100644
    --- a/kernel/time/tick-sched.c
    +++ b/kernel/time/tick-sched.c
    @@ -38,7 +38,9 @@ static ktime_t last_jiffies_update;

    struct tick_sched *tick_get_tick_sched(int cpu)
    {
    - return &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + ts->cpu = cpu;
    + return ts;
    }

    /*
    @@ -137,7 +139,7 @@ __setup("nohz=", setup_tick_nohz);
    static void tick_nohz_update_jiffies(ktime_t now)
    {
    int cpu = smp_processor_id();
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);
    unsigned long flags;

    cpumask_clear_cpu(cpu, nohz_cpu_mask);
    @@ -159,9 +161,10 @@ update_ts_time_stats(struct tick_sched *ts, ktime_t now, u64 *last_update_time)
    ktime_t delta;

    if (ts->idle_active) {
    + int cpu = ts->cpu;
    delta = ktime_sub(now, ts->idle_entrytime);
    ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
    - if (nr_iowait_cpu() > 0)
    + if (nr_iowait_cpu(cpu) > 0)
    ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
    ts->idle_entrytime = now;
    }
    @@ -173,7 +176,7 @@ update_ts_time_stats(struct tick_sched *ts, ktime_t now, u64 *last_update_time)

    static void tick_nohz_stop_idle(int cpu, ktime_t now)
    {
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);

    update_ts_time_stats(ts, now, NULL);
    ts->idle_active = 0;
    @@ -211,7 +214,7 @@ static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
    */
    u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
    {
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);

    if (!tick_nohz_enabled)
    return -1;
    @@ -237,7 +240,7 @@ EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
    */
    u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
    {
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);

    if (!tick_nohz_enabled)
    return -1;
    @@ -267,7 +270,7 @@ void tick_nohz_stop_sched_tick(int inidle)
    local_irq_save(flags);

    cpu = smp_processor_id();
    - ts = &per_cpu(tick_cpu_sched, cpu);
    + ts = tick_get_tick_sched(cpu);

    /*
    * Call to tick_nohz_start_idle stops the last_update_time from being
    @@ -508,7 +511,7 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
    void tick_nohz_restart_sched_tick(void)
    {
    int cpu = smp_processor_id();
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);
    #ifndef CONFIG_VIRT_CPU_ACCOUNTING
    unsigned long ticks;
    #endif
    @@ -671,7 +674,7 @@ static void tick_nohz_kick_tick(int cpu, ktime_t now)
    #if 0
    /* Switch back to 2.6.27 behaviour */

    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);
    ktime_t delta;

    /*
    @@ -688,7 +691,7 @@ static void tick_nohz_kick_tick(int cpu, ktime_t now)

    static inline void tick_check_nohz(int cpu)
    {
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);
    ktime_t now;

    if (!ts->idle_active && !ts->tick_stopped)
    @@ -818,7 +821,7 @@ void tick_setup_sched_timer(void)
    #if defined CONFIG_NO_HZ || defined CONFIG_HIGH_RES_TIMERS
    void tick_cancel_sched_timer(int cpu)
    {
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);

    # ifdef CONFIG_HIGH_RES_TIMERS
    if (ts->sched_timer.base)


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