linux-kernel - Re: [PATCH v3 1/3] rcutorture: Allow a negative value for nfakewriters

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Message-ID: <Z7812CnMT0-NLA4m@pc636>
Date: Wed, 26 Feb 2025 16:40:08 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Uladzislau Rezki <urezki@...il.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Boqun Feng <boqun.feng@...il.com>, RCU <rcu@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Cheung Wall <zzqq0103.hey@...il.com>,
	Neeraj upadhyay <Neeraj.Upadhyay@....com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH v3 1/3] rcutorture: Allow a negative value for
 nfakewriters

On Wed, Feb 26, 2025 at 06:50:02AM -0800, Paul E. McKenney wrote:
> On Wed, Feb 26, 2025 at 03:29:09PM +0100, Uladzislau Rezki wrote:
> > On Tue, Feb 25, 2025 at 04:24:09PM -0500, Joel Fernandes wrote:
> > > On Tue, Feb 25, 2025 at 12:00:18PM +0100, Uladzislau Rezki (Sony) wrote:
> > > > Currently "nfakewriters" parameter can be set to any value but
> > > > there is no possibility to adjust it automatically based on how
> > > > many CPUs a system has where a test is run on.
> > > > 
> > > > To address this, if the "nfakewriters" is set to negative it will
> > > > be adjusted to num_online_cpus() during torture initialization.
> > > > 
> > > > Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
> > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> > > > ---
> > > >  kernel/rcu/rcutorture.c | 22 ++++++++++++++++------
> > > >  1 file changed, 16 insertions(+), 6 deletions(-)
> > > > 
> > > > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > > > index d98b3bd6d91f..f376262532ce 100644
> > > > --- a/kernel/rcu/rcutorture.c
> > > > +++ b/kernel/rcu/rcutorture.c
> > > > @@ -148,6 +148,7 @@ MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, srcu, ...)");
> > > 
> > > IMO, this should also be updated to reflect the possibily to set it negative
> > > and hence to number CPUs:
> > > 
> > > torture_param(int, nfakewriters, 4, "Number of RCU fake writer threads");
> > > 
> > You can set it to a negative as well as to number of CPUs or any other
> > number.
> 
> Joel does have a good point, though.  Could I interest one of you in
> updating the Documentation/admin-guide/kernel-parameters.txt entry for
> rcutorture.nfakewriters?  The rcutorture.nreaders entry is a decent guide.
> 
OK. Then i misunderstood Joel. It was about updating a documentation
about this!

Good point :)

--
Uladzislau Rezki