On Thu, 30 May 2019, Marcelo Tosatti wrote: > On Wed, May 29, 2019 at 04:53:26PM +0200, Anna-Maria Gleixner wrote: > > On Mon, 15 Apr 2019, Marcelo Tosatti wrote: > > > > > --- linux-rt-devel.orig/kernel/time/timer.c 2019-04-15 14:21:02.788704354 -0300 > > > +++ linux-rt-devel/kernel/time/timer.c 2019-04-15 14:22:56.755047354 -0300 > > > @@ -1776,6 +1776,24 @@ > > > if (time_before(jiffies, base->clk)) > > > return; > > > } > > > + > > > +#ifdef CONFIG_PREEMPT_RT_FULL > > > +/* On RT, irq work runs from softirq */ > > > + if (irq_work_needs_cpu()) > > > + goto raise; > > > > So with this patch and the change you made in the patch before, timers on > > RT are expired only when there is pending irq work or after modifying a > > timer on a non housekeeping cpu? > > Well, run_timer_softirq execute only if pending_map contains a bit set. > > > With your patches I could create the following problematic situation on RT > > (if I understood everything properly): I add a timer which should expire in > > 50 jiffies to the wheel of a non housekeeping cpu. So it ends up 50 buckets > > away form now in the first wheel. This timer is the only timer in the wheel > > and the next timer softirq raise is required in 50 jiffies. After adding > > the timer, the timer interrupt is raised, and no timer has to be expired, > > because there is no timer pending. > > But the softirq will be raised, because pending_map will be set: > > + if (!bitmap_empty(base->pending_map, WHEEL_SIZE)) > + goto raise; > > No? I'm sorry! I read the #endif of the CONFIG_PREEMPT_RT_FULL section as an #else... This is where my confusion comes from. I will think about the problem and your solution a little bit more and give you feedback hopefully on monday. Thanks, Anna-Maria
