Messages in this thread | | | Date | Tue, 30 Dec 2014 16:05:36 -0500 | From | Rik van Riel <> | Subject | Re: [PATCH -rt] timer: upper bound on loops of __run_timers processing |
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On 12/30/2014 02:52 PM, 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); + }
It certainly looks like cascading the timers over and over and over again could be a lot of work.
Acked-by: Rik van Riel <riel@redhat.com>
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