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

Marcelo Tosatti
2015-01-14T17:22:12Z

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;
>