Messages in this thread | | | Date | Thu, 23 Apr 2015 15:07:59 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [patch 18/39] tick: sched: Force tick interrupt and get rid of softirq magic |
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On Thu, 23 Apr 2015, Frederic Weisbecker wrote:
> On Wed, Apr 22, 2015 at 04:32:11PM +0200, Thomas Gleixner wrote: > > On Wed, 22 Apr 2015, Frederic Weisbecker wrote: > > > But the reprogramming happens only under "if ((long)delta_jiffies >= 1)". > > > Probably this condition should go away as well. > > > > Errm. > > > > if (!ts->tick_stopped && delta_jiffies <= 1) > > goto out; > > > > So if the tick is NOT stopped and delta_jiffies <= 1 we let it tick > > and do nothing. > > > > if (delta_jiffies >= 1) > > Do the magic nohz stuff > > else > > tick_nohz_restart() > > > > We want the distinction here because if the tick IS stopped and the > > next event is due we need to kick it into gear again. So the condition > > needs to stay. It probably should be if (delta > 1), but that's a > > different story. > > Yes but what if the tick is stopped already and delta_jiffies < 1? Say the > tick was last programmed to fire in 5 seconds. An irq fires and enqueues > a timer to fire now. If it's soon enough that delta_jiffies < 1, it seems > we are missing the clock reprogramming and even the softirq from that irq exit. > > Because we have: > > if (!ts->tick_stopped && delta_jiffies <= 1) > goto out; > > if ((long)delta_jiffies >= 1) { > //do clock reprogramming or restart > ... > } > > - raise_softirq(TIMER_SOFTIRQ);
Did you actually read what I wrote?
> > if (delta_jiffies >= 1) > > Do the magic nohz stuff > > else > > tick_nohz_restart()
So if ticked is stopped AND delta < 1 we call tick_nohz_restart(). Which will programm the tick for the next possible period to expire. Which will kick the timer softirq and expire the timer.
Thanks,
tglx
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