linux-kernel - Re: [PATCH] rcutorture: Select from only online CPUs

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Date:   Mon, 25 Mar 2019 12:33:37 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kselftest <linux-kselftest@...r.kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Shuah Khan <shuah@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] rcutorture: Select from only online CPUs

On Mon, Mar 25, 2019 at 11:02 AM Paul E. McKenney <paulmck@...ux.ibm.com> wrote:
>
> On Fri, Mar 22, 2019 at 11:46:19PM -0400, Joel Fernandes (Google) wrote:
> > The rcutorture jitter.sh script selects a random CPU but does not check
> > if it is offline or online. This leads to taskset errors many times. On
> > my machine, hyper threading is disabled so half the cores are offline
> > causing taskset errors a lot of times. Let us fix this by checking from
> > only the online CPUs on the system.
> >
> > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
>
> Good catch!
>
> Please see below for one suggestion for simplification.
>
>                                                         Thanx, Paul
>
> > ---
> >  tools/testing/selftests/rcutorture/bin/jitter.sh | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/rcutorture/bin/jitter.sh b/tools/testing/selftests/rcutorture/bin/jitter.sh
> > index 3633828375e3..53bf9d99b5cd 100755
> > --- a/tools/testing/selftests/rcutorture/bin/jitter.sh
> > +++ b/tools/testing/selftests/rcutorture/bin/jitter.sh
> > @@ -47,10 +47,19 @@ do
> >               exit 0;
> >       fi
> >
> > -     # Set affinity to randomly selected CPU
> > +     # Set affinity to randomly selected online CPU
> >       cpus=`ls /sys/devices/system/cpu/*/online |
>
>         cpus=`grep 1 /sys/devices/system/cpu/*/online |
>

Yes, this is better. Lets do it this way :)

> >               sed -e 's,/[^/]*$,,' -e 's/^[^0-9]*//' |
> >               grep -v '^0*$'`
>
> Of course, now I have no idea why I excluded CPU 0...  :-/

Yes, I was wondering as well about that :-)

thanks,

 - Joel