linux-kernel - Re: [PATCH v2] rcu: Allow to eliminate softirq processing from rcutree

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Message-Id: <20190320181210.GO4102@linux.ibm.com>
Date:   Wed, 20 Mar 2019 11:12:10 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, tglx@...utronix.de,
        Mike Galbraith <efault@....de>
Subject: Re: [PATCH v2] rcu: Allow to eliminate softirq processing from
 rcutree

On Wed, Mar 20, 2019 at 06:59:52PM +0100, Sebastian Andrzej Siewior wrote:
> On 2019-03-20 10:30:01 [-0700], Paul E. McKenney wrote:
> > On Wed, Mar 20, 2019 at 05:35:32PM +0100, Sebastian Andrzej Siewior wrote:
> > > On 2019-03-20 09:15:00 [-0700], Paul E. McKenney wrote:
> > > > I am considering making it a module_param() to avoid namespace pollution,
> > > > as it would become something like rcutree.nosoftirq.
> > > > 
> > > > Thoughts?
> > > 
> > > nope, perfect.
> > 
> > Please see below for an untested patch.  Thoughts?
> 
> > -	if (rcu_softirq_enabled) {
> > +	if (!nosoftirq) {
> >  		raise_softirq(RCU_SOFTIRQ);
> >  	} else {
> 
> This double negation looks weird. Can we flip the logic somehow?
> /me testing if it works…

We could name it something like "use_softirq" and initialize it to true.
I am OK either way.

							Thanx, Paul