On Mon, Apr 15, 2019 at 05:12:15PM -0300, Marcelo Tosatti wrote: > Check base->pending_map locklessly and skip raising timer softirq > if empty. > > What allows the lockless (and potentially racy against mod_timer) > check is that mod_timer will raise another timer softirq after > modifying base->pending_map. > > Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx> > > --- > kernel/time/timer.c | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > Index: linux-rt-devel/kernel/time/timer.c > =================================================================== > --- 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; > +#endif > + base = this_cpu_ptr(&timer_bases[BASE_STD]); > + if (!housekeeping_cpu(base->cpu, HK_FLAG_TIMER)) { > + if (!bitmap_empty(base->pending_map, WHEEL_SIZE)) > + goto raise; > + base++; Shall we check against CONFIG_NO_HZ_COMMON? Otherwise the base could point to something else rather tha the deferred base (NR_BASES==1 if without nohz-common). I see that run_local_timers() has similar pattern, actually I'm thinking whether we can put things like "base++" to be inside some "if"s of CONFIG_NO_HZ_COMMON to be clear. Thanks, -- Peter Xu