Re: [PATCH -rt] timer: upper bound on loops of __run_timers processing

Marcelo Tosatti
2015-01-26T21:13:03Z

Ping ?

On Wed, Jan 14, 2015 at 03:21:47PM -0200, Marcelo Tosatti wrote:
>
> Ping?
>
> On Tue, Dec 30, 2014 at 05:52:28PM -0200, Marcelo Tosatti wrote:
> >
> > Commit "timers: do not raise softirq unconditionally", allows for timer
> > wheel processing (__run_timers) to be delayed for long periods of time.
> >
> > The effect is that
> >
> > loops = jiffies - base->timer_jiffies
> >
> > Can grow to very large values resulting in __run_timers taking hundreds
> > of milliseconds to execute.
> >
> > Fix by creating an upper bound on the number of loops to be processed.
> > This allows a nohz=off kernel to achieve desired latencies.
> >
> > Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> >
> > diff --git a/kernel/timer.c b/kernel/timer.c
> > index f59e18c..c128416 100644
> > --- a/kernel/timer.c
> > +++ b/kernel/timer.c
> > @@ -1488,6 +1488,12 @@ void run_local_timers(void)
> > }
> > #endif
> >
> > + if (time_after_eq(jiffies, base->timer_jiffies)) {
> > + unsigned long jiffies_delta = jiffies - base->timer_jiffies;
> > + if (jiffies_delta > TVR_SIZE)
> > + raise_softirq(TIMER_SOFTIRQ);
> > + }
> > +
> > if (!base->active_timers)
> > goto out;
> >
> --
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