Re: [PATCH 1/4] rcutorture: Allow a negative value for nfakewriters

["Paul E. McKenney" <paulmck@kernel.org>]

On Tue, Jan 28, 2025 at 09:55:19PM +0100, Uladzislau Rezki wrote:
> Hello, Paul!
> 
> > 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_possible_cpus() during torture initialization.
> > 
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > ---
> >  kernel/rcu/rcutorture.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > index d26fb1d33ed9..6bc161e1e8ac 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -4050,6 +4050,10 @@ rcu_torture_init(void)
> >  					  writer_task);
> >  	if (torture_init_error(firsterr))
> >  		goto unwind;
> > +
> > +	if (nfakewriters < 0)
> > +		nfakewriters = (int) num_possible_cpus();
> > +
> >  	if (nfakewriters > 0) {
> >  		fakewriter_tasks = kcalloc(nfakewriters,
> >  					   sizeof(fakewriter_tasks[0]),
> > -- 
> > 2.39.5
> > 
> 
> Don't you mind to take this as well? It is needed for:
> 
> rcu: Update TREE05.boot to test normal synchronize_rcu()

I would, but could you please set something up like we have for
nreaders (the module parameter) and nrealreaders (the value actually
used throughout).  I freely admit that nrealfakereaders sounds a bit
strange, so please feel free to either embrace the strangeness or propose
an alternative.  ;-)

The reason for this is so that, on a system with 128 CPUs, the user can
distinguish between having specified (say) nfakewriters=128 on the one
hand or nfakewriters=-1 on the other.

							Thanx, Paul