From: Clark Williams <williams@redhat.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Phil Edworthy <phil.edworthy@renesas.com>,
rt-users <linux-rt-users@vger.kernel.org>,
John Kacur <jkacur@gmail.com>, Carsten Emde <C.Emde@osadl.org>
Subject: Re: cyclictest result variations
Date: Wed, 28 Mar 2018 10:31:56 -0500 [thread overview]
Message-ID: <20180328103156.61721154@tagon> (raw)
In-Reply-To: <87370kqmec.fsf@linutronix.de>
On Wed, 28 Mar 2018 16:56:27 +0200
John Ogness <john.ogness@linutronix.de> wrote:
> On 2018-03-28, Phil Edworthy <phil.edworthy@renesas.com> wrote:
> >> > I found that cyclictest results vary from one run to another.
> >> >
> >> > [...]
> >> >
> >> > Is it common knowledge that cyclictest results vary so much from
> >> > one run to another? Any ideas how to mitigate this?
> >>
> >> It would be helpful if you provided the command arguments you use for
> >> your tests. Particularly important options to consider:
> >>
> >> -a / --affinity
> >> -m / --mlockall
> >> -n / --nanosleep
> >> -t / --threads
> >> --secaligned
> >>
> >> and of course giving it an appropriate realtime priority:
> >>
> >> -p / --priority
> >
> > Sure:
> > cyclictest -m -n -Sp99 -i200 -h300 -M -D 10h
>
> I would recommend using prio 98 instead of 99. In general, applications
> should not be taking the CPU from the migration or watchdog tasks. And
> usually you want cyclictest to reflect the latencies of real
> applications.
Agree, please don't use fifo:99. Honestly there's no difference between fifo:51
and fifo:98. The interrupt threads default to fifo:50, so you want to be above that
but no real need to contend with migration, watchdog or posix timers.
Also, if you are on a NUMA architecture system, you may want to use the
--numa/-U option, instead of the --smp/-S option. With that option cyclictest
uses the libnuma calls to allocate a stack on the local NUMA node for each
measurement thread (trying to avoid cross-node allocations).
Clark
parent reply other threads:[~2018-03-28 15:32 UTC|newest]
Thread overview: expand[flat|nested] mbox.gz Atom feed
[parent not found: <87370kqmec.fsf@linutronix.de>]
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