Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH v3 2/2] sched: Add a check for cpu unbound deferrable timers | Date | Wed, 06 May 2020 16:03:34 +0200 |
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Prasad Sodagudi <psodagud@codeaurora.org> writes:
> Subject: sched: Add...
How is this related to the scheduler?
> Add a check to find expired unbound deferrable timers > and trigger softirq for handling timers. This way a CPU > can process all the expired deferrable timers whenever > it is out off idle state due to an interrupt.
A little bit more context would be useful.
> Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org> > --- > include/linux/timer.h | 3 +++ > kernel/time/tick-sched.c | 8 +++++++- > kernel/time/timer.c | 29 ++++++++++++++++++++++++++++- > 3 files changed, 38 insertions(+), 2 deletions(-) > > diff --git a/include/linux/timer.h b/include/linux/timer.h > index 0dc19a8..e85dd2d 100644 > --- a/include/linux/timer.h > +++ b/include/linux/timer.h > @@ -172,6 +172,9 @@ extern int del_timer(struct timer_list * timer); > extern int mod_timer(struct timer_list *timer, unsigned long expires); > extern int mod_timer_pending(struct timer_list *timer, unsigned long expires); > extern int timer_reduce(struct timer_list *timer, unsigned long expires); > +#ifdef CONFIG_SMP
This #ifdef is useless because ...
> +extern bool check_pending_deferrable_timers(int cpu); > +#endif > > /* > * The jiffies value which is added to now, when there is no timer > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 3e2dc9b..16aec80 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -23,6 +23,7 @@ > #include <linux/module.h> > #include <linux/irq_work.h> > #include <linux/posix-timers.h> > +#include <linux/timer.h> > #include <linux/context_tracking.h> > #include <linux/mm.h> > > @@ -1274,8 +1275,13 @@ static inline void tick_nohz_irq_enter(void) > now = ktime_get(); > if (ts->idle_active) > tick_nohz_stop_idle(ts, now); > - if (ts->tick_stopped) > + if (ts->tick_stopped) { > tick_nohz_update_jiffies(now); > +#ifdef CONFIG_SMP > + if (check_pending_deferrable_timers(smp_processor_id())) > + raise_softirq_irqoff(TIMER_SOFTIRQ); > +#endif
... you failed to provide a stub function which avoids this #ifdef
> + } > } > > #else > diff --git a/kernel/time/timer.c b/kernel/time/timer.c > index 1bf9b49..5947c63 100644 > --- a/kernel/time/timer.c > +++ b/kernel/time/timer.c > @@ -221,6 +221,7 @@ static DECLARE_WORK(timer_update_work, timer_update_keys); > > #ifdef CONFIG_SMP > struct timer_base timer_base_deferrable; > +static atomic_t deferrable_pending; > unsigned int sysctl_timer_migration = 1; > > DEFINE_STATIC_KEY_FALSE(timers_migration_enabled); > @@ -1610,6 +1611,31 @@ static u64 cmp_next_hrtimer_event(u64 basem, u64 expires) > return DIV_ROUND_UP_ULL(nextevt, TICK_NSEC) * TICK_NSEC; > } > > + > +#ifdef CONFIG_SMP > +/* > + * check_pending_deferrable_timers - Check for unbound deferrable timer expiry > + * @cpu - Current CPU
Bogus doc format.
> + * > + * The function checks whether any global deferrable pending timers > + * are exipired or not. This function does not check cpu bounded > + * diferrable pending timers expiry.
Editors have spell check.
> + * > + * The function returns true when a cpu unbounded deferrable timer is expired. > + */ > +bool check_pending_deferrable_timers(int cpu) > +{ > + if (cpu == tick_do_timer_cpu || > + tick_do_timer_cpu == TICK_DO_TIMER_NONE) {
The second line conditional wants to be aligned with the first line conditional.
> + if (time_after_eq(jiffies, timer_base_deferrable.clk) > + && !atomic_cmpxchg(&deferrable_pending, 0, 1)) {
Ditto. Aside of that this deferrable pending magic lacks any form of explanation.
> + return true; > + } > + } > + return false; > +} > +#endif > + > /** > * get_next_timer_interrupt - return the time (clock mono) of the next timer > * @basej: base time jiffies > @@ -1801,7 +1827,8 @@ static __latent_entropy void run_timer_softirq(struct softirq_action *h) > if (IS_ENABLED(CONFIG_NO_HZ_COMMON)) { > __run_timers(this_cpu_ptr(&timer_bases[BASE_DEF])); > #ifdef CONFIG_SMP > - if (tick_do_timer_cpu == TICK_DO_TIMER_NONE || > + if ((atomic_cmpxchg(&deferrable_pending, 1, 0) &&
How is that supposed to compile with NOHZ=n?
For every version of these patches the 0-day robot is complaining about exactly the same problem:
Your testing is solely done with one config, i.e. the config you are interested in.
Is it really so hard to compile test for a total of 4 combinations of SMP and NOHZ?
Thanks,
tglx
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