linux-kernel - Re: [Query]: Timer overflow events on core isolated with NO_HZ

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Message-ID: <CAKohpokQ52nrO9JrQhohsH78=mbJyaC4eBK4DwvO1Azfz9vEGg@mail.gmail.com>
Date:	Tue, 7 Jan 2014 20:31:52 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Kevin Hilman <khilman@...aro.org>,
	Frédéric Weisbecker <fweisbec@...il.com>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [Query]: Timer overflow events on core isolated with NO_HZ_FULL

Missed lists earlier :(

On 7 January 2014 20:31, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> Hi Kevin/Frederic,
>
> In my traces I see a guaranteed interrupt on the isolated
> core, which is running under NO_HZ_FULL mode and is
> running a single thread "stress", after ~90 seconds.
>
> When I look into the traces I see we get only two events:
> - irq-handler-entry
> - irq-handler-exit
>
> And no more detail is available in the traces, system again
> goes to no interruption mode for next 90 seconds.
>
> I hope this is because the timers we have queued for long
> enough times are getting overflowed? I tried to enable
> cpusets and then see which timers are active on CPU1 from
> /proc/timer_list and that gave me:
>
> tick_sched_timer and it_real_fn. These are probably queued
> for long enough times, around 450 seconds and 2000 seconds.
>
> So, my question is: Why are these getting queued? And how
> can I get rid of those for my case, where I want zero interruption
> on isolated core, as that would be running a userspace thread
> to handle data plane packets.
>
>
> Another thing I tried out recently was to make my single threaded
> task "stress" a real time task with priority 99 (along with cpusets).
> But it seems there are more than one thread getting on that CPU
> and so tick occurs immediately.
>
> I tried to call "stress" with help of chrt.
>
> --
> viresh
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