From: Marcelo Tosatti <mtosatti@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Anna-Maria Behnsen <anna-maria@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <frederic@kernel.org>,
Peter Xu <peterx@redhat.com>,
Nitesh Narayan Lal <nitesh@redhat.com>,
Alex Belits <abelits@marvell.com>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
John Stultz <john.stultz@linaro.org>
Subject: Re: [patch 8/8] hrtimer: Avoid more SMP function calls in clock_was_set()
Date: Tue, 27 Apr 2021 12:11:25 -0300 [thread overview]
Message-ID: <20210427151125.GA171315@fuller.cnet> (raw)
In-Reply-To: <20210427083724.840364566@linutronix.de>
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?
next prev parent reply other threads:[~2021-04-27 15:12 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-27 8:25 [patch 0/8] hrtimers: Overhaul the clock_was_set() logic Thomas Gleixner
2021-04-27 8:25 ` [patch 1/8] hrtimer: Ensure timerfd notification for HIGHRES=n Thomas Gleixner
2021-04-27 8:25 ` [patch 2/8] hrtimer: Force clock_was_set() handling for the HIGHRES=n, NOHZ=y case Thomas Gleixner
2021-05-12 14:59 ` Peter Zijlstra
2021-05-12 16:40 ` Thomas Gleixner
2021-04-27 8:25 ` [patch 3/8] timerfd: Provide timerfd_resume() Thomas Gleixner
2021-04-27 8:25 ` [patch 4/8] timekeeping: Distangle resume and clock-was-set events Thomas Gleixner
2021-04-27 8:25 ` [patch 5/8] time/timekeeping: Avoid invoking clock_was_set() twice Thomas Gleixner
2021-04-27 8:25 ` [patch 6/8] hrtimer: Add bases argument to clock_was_set() Thomas Gleixner
2021-04-27 8:25 ` [patch 7/8] hrtimer: Avoid unnecessary SMP function calls in clock_was_set() Thomas Gleixner
2021-05-13 14:59 ` Peter Zijlstra
2021-05-14 18:52 ` Thomas Gleixner
2021-05-14 23:28 ` Peter Zijlstra
2021-05-15 0:24 ` Thomas Gleixner
2021-04-27 8:25 ` [patch 8/8] hrtimer: Avoid more " Thomas Gleixner
2021-04-27 15:11 ` Marcelo Tosatti [this message]
2021-04-27 19:59 ` Thomas Gleixner
2021-04-30 7:12 ` [patch V2 " Thomas Gleixner
2021-04-30 16:49 ` Marcelo Tosatti
2021-05-13 7:47 ` Peter Zijlstra
2021-05-14 19:08 ` Thomas Gleixner
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