linux-kernel - Re: [Query] Ticks happen in pair for NO_HZ

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Date:	Tue, 17 Dec 2013 16:05:29 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Kevin Hilman <khilman@...aro.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Linaro Networking <linaro-networking@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [Query] Ticks happen in pair for NO_HZ_FULL cores ?

Sorry for the delay, was on holidays..

On 11 December 2013 18:52, Frederic Weisbecker <fweisbec@...il.com> wrote:
> On Tue, Dec 03, 2013 at 01:57:37PM +0530, Viresh Kumar wrote:
>> - again got arch_timer interrupt after 5 ms (HZ=200)
>
> Right, looking at the details, the 2nd interrupt is caused by workqueue delayed
> work bdi writeback.

I am not that great at reading traces or kernelshark output, but I
still feel I haven't
seen anything wrong. And I wasn't talking about the delayed workqueue here..

I am looking at the trace I attached with kernelshark after filtering
out CPU0 events:
- Event 41, timestamp: 159.891973
- it ends at event 56, timestamp: 159.892043

And after that the next event comes after 5 Seconds.

And so I was talking for the Event 41.

>> So the query is: why don't we check that at the end of servicing vmstat
>> stuff and migrating back to "stress" ??
>
> I fear I don't understand your question. Do you mean why don't we prevent from
> that bdi writeback work to run when we are in full dynticks mode?

No..
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