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

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Date:   Tue, 26 Mar 2019 14:35:49 -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 Tue, Mar 26, 2019 at 09:01:40AM -0700, Paul E. McKenney wrote:
> On Mon, Mar 25, 2019 at 06:40:17PM -0400, Joel Fernandes wrote:
> > On Mon, Mar 25, 2019 at 12:42 PM Paul E. McKenney <paulmck@...ux.ibm.com> wrote:
> > >
> > > On Mon, Mar 25, 2019 at 12:33:37PM -0400, Joel Fernandes wrote:
> > > > 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 :-)
> > >
> > > Please feel free to try including CPU 0 and running the set of single-CPU
> > > rcutorture scenarios.  ;-)
> > 
> > Will do and then will update the patch by adding the CPU back, if all
> > is well. Thanks.
> 
> And rcutorture doesn't like the rcu_is_cpu_rrupt_from_idle() patch on
> scenarios SRCU-P, TASKS01, and TREE05, which are the Tree RCU scenarios
> that enable CONFIG_PROVE_RCU.  The compiler error is:
> 
> kernel/rcu/tree.c:391:2: error: implicit declaration of function ‘_this_cpu_read’ [-Werror=implicit-function-declaration]
> 
> My guess is that the initial underscore needs to go.  I will drop
> these two patches in favor of an update from you.  ;-)

Sorry, I fixed that up and running tests now.

By the way, may be you decided to not run the jitter on CPU0 just because on
some systems, CPU0 does not have an 'online' file? In this case, the grep may
throw errors I guess which troubles the script.

>From the old cpu hotplug docs, I found that if CONFIG_BOOTPARAM_HOTPLUG_CPU0
or cpu0_hotplug boot command line option is not passed, then cpu0 cannot be
offlined in which case, presumably the 'online' file will be missing, like
some systems I am testing on.

thanks,

 - Joel