Messages in this thread | | | Date | Thu, 23 Apr 2015 18:14:14 +0200 | From | Frederic Weisbecker <> | Subject | Re: [patch 18/39] tick: sched: Force tick interrupt and get rid of softirq magic |
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On Thu, Apr 23, 2015 at 03:07:59PM +0200, Thomas Gleixner wrote: > 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.
Right, I missed the "else" that moved.
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