Messages in this thread | | | Date | Tue, 27 Apr 2021 12:11:25 -0300 | From | Marcelo Tosatti <> | Subject | Re: [patch 8/8] hrtimer: Avoid more SMP function calls in clock_was_set() |
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On Tue, Apr 27, 2021 at 10:25:45AM +0200, Thomas Gleixner wrote: > There are more indicators whether the SMP function calls on clock_was_set() > can be avoided: > > - When the remote CPU is currently handling hrtimer_interrupt(). In > that case the remote CPU will update offsets and reevaluate the timer > bases before reprogramming anyway, so nothing to do. > > By unconditionally updating the offsets the following checks are possible: > > - When the offset update already happened on the remote CPU then the > remote update attempt will yield the same seqeuence number and no > IPI is required. > > - After updating it can be checked whether the first expiring timer in > the affected clock bases moves before the first expiring (softirq) > timer of the CPU. If that's not the case then sending the IPI is not > required. > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > --- > kernel/time/hrtimer.c | 66 +++++++++++++++++++++++++++++++++++++++++++------- > 1 file changed, 57 insertions(+), 9 deletions(-) > > --- a/kernel/time/hrtimer.c > +++ b/kernel/time/hrtimer.c > @@ -880,6 +880,60 @@ static void hrtimer_reprogram(struct hrt > tick_program_event(expires, 1); > } > > +static bool update_needs_ipi(struct hrtimer_cpu_base *cpu_base, > + unsigned int active) > +{ > + struct hrtimer_clock_base *base; > + unsigned int seq; > + ktime_t expires; > + > + /* > + * If the remote CPU is currently handling an hrtimer interrupt, it > + * will update and reevaluate the first expiring timer of all clock > + * bases before reprogramming. Nothing to do here. > + */ > + if (cpu_base->in_hrtirq) > + return false;
Thomas,
The base offsets are updated at
Cscope tag: hrtimer_update_base # line filename / context / line 1 736 kernel/time/hrtimer.c <<retrigger_next_event>> (IPI handler) hrtimer_update_base(base); 2 1617 kernel/time/hrtimer.c <<hrtimer_run_softirq>> (softirq handler) now = hrtimer_update_base(cpu_base); 3 1645 kernel/time/hrtimer.c <<hrtimer_interrupt>> (hrtimer_interrupt entry) entry_time = now = hrtimer_update_base(cpu_base); 4 1695 kernel/time/hrtimer.c <<hrtimer_interrupt>> (after tick_program_event failure) now = hrtimer_update_base(cpu_base); 5 1768 kernel/time/hrtimer.c <<hrtimer_run_queues>> (sched_tick) now = hrtimer_update_base(cpu_base);
Consider
hrtimer_interrupt in_hrtirq = 1 __run_hrtimer raw_spin_unlock_irqrestore(&cpu_base->lock, flags) settimeofday clock_was_set lock cpu_base->lock update_needs_ipi returns false continue to process hrtimers with stale base->offset
No?
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