linux-kernel - Re: [RFC PATCH 12/12] rcu: Nocb (de)activate through sysfs

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Message-ID: <20200923190050.GA1026@lenoir>
Date:   Wed, 23 Sep 2020 21:00:50 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>
Subject: Re: [RFC PATCH 12/12] rcu: Nocb (de)activate through sysfs

On Wed, Sep 23, 2020 at 08:47:16AM -0700, Paul E. McKenney wrote:
> On Wed, Sep 23, 2020 at 05:27:46PM +0200, Frederic Weisbecker wrote:
> > On Mon, Sep 21, 2020 at 05:26:29PM -0700, Paul E. McKenney wrote:
> > > On Mon, Sep 21, 2020 at 02:43:51PM +0200, Frederic Weisbecker wrote:
> > > > Not for merge.
> > > > 
> > > > Make nocb toggable for a given CPU using:
> > > > 	/sys/devices/system/cpu/cpu*/hotplug/nocb
> > > > 
> > > > This is only intended for those who want to test this patchset. The real
> > > > interfaces will be cpuset/isolation and rcutorture.
> > > 
> > > Excellent choice for testing in the near term!
> > > 
> > > How does rcutorture fare with this series if an additional kthread toggles
> > > offloading on and off continually?
> > 
> > So yeah that would be the plan: having something that randomly toggles
> > offloading from the RCU tests themselves. I'm not quite familiar with
> > rcutorture internals yet though.
> 
> If you supply a function that selects a CPU and does the toggle, I
> can quickly and easily wire it into rcutorture.  I of course have no
> objection to your learning to do this yourself, but the offer stands.

I gladly accept your proposal! This way I will integrate it in the set
and start testing.

The functions to call would be:

void rcu_nocb_cpu_offload(int cpu);
void rcu_nocb_cpu_deoffload(int cpu);


> 
> > > All questions and concerns aside, excellent progress and nice work!!!
> > 
> > Thanks! We are slowly making progress :)
> 
> Better than quickly failing to make progress, to be sure!  ;-)

;-)

Thanks a lot!