On Tue, Jun 04, 2019 at 02:29:31PM +0800, Peter Xu wrote: > 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 <[email protected]> > > > > --- > > 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
Hi Peter, Yes, that is a good point and needs fixing. I'll wait for Anna's comments before posting -v2.
