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Date: Thu, 20 Apr 2017 19:56:22 +0200 (CEST) From: Thomas Gleixner <tglx@...utronix.de> To: Frederic Weisbecker <fweisbec@...il.com> cc: Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>, Rik van Riel <riel@...hat.com>, James Hartsock <hartsjc@...hat.com>, stable@...r.kernel.org, Tim Wright <tim@...bash.co.uk>, Pavel Machek <pavel@....cz> Subject: Re: [PATCH 2/2] tick: Make sure tick timer is active when bypassing reprogramming On Thu, 20 Apr 2017, Frederic Weisbecker wrote: > So far we have run into too much troubles with the optimization path > that skips reprogramming the clock on IRQ exit when the expiration > deadline hasn't changed. If by accident the cached deadline happens to > be out of sync with the hardware deadline, the buggy result and its > cause are hard to investigate. So lets detect and warn about the issue > early. > > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com> > Cc: Tim Wright <tim@...bash.co.uk> > Cc: Pavel Machek <pavel@....cz> > Cc: James Hartsock <hartsjc@...hat.com> > Cc: Peter Zijlstra <peterz@...radead.org> > Cc: Rik van Riel <riel@...hat.com> > Cc: Thomas Gleixner <tglx@...utronix.de> > Cc: Ingo Molnar <mingo@...nel.org> > --- > kernel/time/tick-sched.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 502b320..eb1366e 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -783,8 +783,10 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, > tick = expires; > > /* Skip reprogram of event if its not changed */ > - if (ts->tick_stopped && (expires == ts->next_tick)) > + if (ts->tick_stopped && (expires == ts->next_tick)) { > + WARN_ON_ONCE(dev->next_event > ts->next_tick); What about handling it proper ? dev->next_event might be KTIME_MAX, i.e. no more event for the next 500+ years. Thanks, tglx
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