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    SubjectRe: [PATCH v5 2/2] sched: make update_cpu_load_nohz() consider missed ticks in NOHZ_FULL
    On Tue, Nov 10, 2015 at 09:36:02AM +0900, byungchul.park@lge.com wrote:
    > From: Byungchul Park <byungchul.park@lge.com>
    >
    > Usually tick can be stopped for an idle cpu in NOHZ. However in NOHZ_FULL,
    > a non-idle cpu's tick also can be stopped. However, update_cpu_load_nohz()
    > does not consider the case a non-idle cpu's tick has been stopped at all.
    >
    > This patch makes the update_cpu_load_nohz() know if the calling path comes
    > from NOHZ_FULL or idle NOHZ.
    >
    > Signed-off-by: Byungchul Park <byungchul.park@lge.com>
    > Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
    > ---
    > include/linux/sched.h | 4 ++--
    > kernel/sched/fair.c | 10 ++++++----
    > kernel/time/tick-sched.c | 8 ++++----
    > 3 files changed, 12 insertions(+), 10 deletions(-)
    >
    > diff --git a/include/linux/sched.h b/include/linux/sched.h
    > index 699228b..f1b59aa 100644
    > --- a/include/linux/sched.h
    > +++ b/include/linux/sched.h
    > @@ -177,9 +177,9 @@ extern void get_iowait_load(unsigned long *nr_waiters, unsigned long *load);
    > extern void calc_global_load(unsigned long ticks);
    >
    > #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
    > -extern void update_cpu_load_nohz(void);
    > +extern void update_cpu_load_nohz(int active);
    > #else
    > -static inline void update_cpu_load_nohz(void) { }
    > +static inline void update_cpu_load_nohz(int active) { }
    > #endif
    >
    > extern unsigned long get_parent_ip(unsigned long addr);
    > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    > index 7760678..3d93756 100644
    > --- a/kernel/sched/fair.c
    > +++ b/kernel/sched/fair.c
    > @@ -4419,10 +4419,11 @@ static void update_idle_cpu_load(struct rq *this_rq)
    > /*
    > * Called from tick_nohz_idle_exit() -- try and fix up the ticks we missed.
    > */
    > -void update_cpu_load_nohz(void)
    > +void update_cpu_load_nohz(int active)
    > {
    > struct rq *this_rq = this_rq();
    > unsigned long curr_jiffies = READ_ONCE(jiffies);
    > + unsigned long load = active ? weighted_cpuload(cpu_of(this_rq)) : 0;

    Hello,

    I added this part after you acked.. What do you think about this
    modification?

    > unsigned long pending_updates;
    >
    > if (curr_jiffies == this_rq->last_load_update_tick)
    > @@ -4433,10 +4434,11 @@ void update_cpu_load_nohz(void)
    > if (pending_updates) {
    > this_rq->last_load_update_tick = curr_jiffies;
    > /*
    > - * We were idle, this means load 0, the current load might be
    > - * !0 due to remote wakeups and the sort.
    > + * In the regular NOHZ case, we were idle, this means load 0.
    > + * In the NOHZ_FULL case, we were non-idle, we should consider
    > + * its weighted load.

    This, too.

    > */
    > - __update_cpu_load(this_rq, 0, pending_updates, 0);
    > + __update_cpu_load(this_rq, load, pending_updates, active);

    This, too.

    Thank you,
    byungchul

    > }
    > raw_spin_unlock(&this_rq->lock);
    > }
    > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
    > index 7c7ec45..515edf3 100644
    > --- a/kernel/time/tick-sched.c
    > +++ b/kernel/time/tick-sched.c
    > @@ -694,11 +694,11 @@ out:
    > return tick;
    > }
    >
    > -static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
    > +static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now, int active)
    > {
    > /* Update jiffies first */
    > tick_do_update_jiffies64(now);
    > - update_cpu_load_nohz();
    > + update_cpu_load_nohz(active);
    >
    > calc_load_exit_idle();
    > touch_softlockup_watchdog();
    > @@ -725,7 +725,7 @@ static void tick_nohz_full_update_tick(struct tick_sched *ts)
    > if (can_stop_full_tick())
    > tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
    > else if (ts->tick_stopped)
    > - tick_nohz_restart_sched_tick(ts, ktime_get());
    > + tick_nohz_restart_sched_tick(ts, ktime_get(), 1);
    > #endif
    > }
    >
    > @@ -916,7 +916,7 @@ void tick_nohz_idle_exit(void)
    > tick_nohz_stop_idle(ts, now);
    >
    > if (ts->tick_stopped) {
    > - tick_nohz_restart_sched_tick(ts, now);
    > + tick_nohz_restart_sched_tick(ts, now, 0);
    > tick_nohz_account_idle_ticks(ts);
    > }
    >
    > --
    > 1.7.9.5
    >
    > --
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