From: Chris Friesen <chris.friesen@windriver.com>
To: <rolf.freitag@email.de>, <linux-rt-users@vger.kernel.org>
Subject: Re: Why is real time pinging not possible with RT kernels?
Date: Sun, 11 Jun 2017 23:10:41 -0600 [thread overview]
Message-ID: <593E2251.3070308@windriver.com> (raw)
In-Reply-To: <trinity-c4969a6b-8eeb-4799-93a4-349c300c9363-1497118391298@3capp-webde-bap09>
On 06/10/2017 12:13 PM, rolf.freitag@email.de wrote:
> Hi,
>
> I tried ping as a minimal latency test, e. g.
>
> ionice -c3 -p $$
> renice +19 -p $$
> ping -q -s 28 -l 1 -p 0f1e2d3c4b5a6978 -i 0.001 localhost
>
> but when cyclictest shows a worst-case latency of 40 mikroseconds,
> ping shows more than 10,000 (after 1 day run).
> I tried different kernels, e. g.
> SMP PREEMPT RT Debian 4.6.4-1~bpo8+1 (2016-08-11) x86_64
> but with the same result, low cyclictest values, high ping values.
> What is the reason?
That's a great question, I'm curious what responses you get.
It might be useful to use a custom ping client (or remove the -q option and
parse the output) so you could track the latencies and generate a histogram to
see if that 10ms latency was a single outlier or whether it happened fairly
frequently.
Chris
next prev parent reply other threads:[~2017-06-12 5:10 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-10 18:13 Why is real time pinging not possible with RT kernels? rolf.freitag
2017-06-12 5:10 ` Chris Friesen [this message]
2017-06-12 12:57 ` Corey Minyard
2017-06-12 13:17 ` Peter C. Wallace
2017-06-12 16:45 ` Chris Friesen
2017-06-12 17:16 ` Corey Minyard
2017-06-17 8:37 ` rolf.freitag
2017-06-17 12:10 ` Corey Minyard
2017-06-13 11:58 ` Sebastian Andrzej Siewior
2017-06-13 16:06 ` Chris Friesen
2017-06-13 16:53 ` Corey Minyard
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