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Message-ID: <20150114172147.GA16570@amt.cnet>
Date: Wed, 14 Jan 2015 15:21:47 -0200
From: Marcelo Tosatti <mtosatti@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>,
Steven Rostedt <rostedt@...dmis.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Clark Williams <clark.williams@...il.com>,
Luiz Capitulino <lcapitulino@...hat.com>,
Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
linux-rt-users@...r.kernel.org
Subject: Re: [PATCH -rt] timer: upper bound on loops of __run_timers
processing
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@...hat.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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