linux-kernel - Re: [PATCH 2/4] torture: Remove CONFIG_NR

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Message-ID: <d410ab83-515a-4454-8420-1ada8cf86efd@paulmck-laptop>
Date: Fri, 24 Jan 2025 07:45:23 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Uladzislau Rezki <urezki@...il.com>
Cc: 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 2/4] torture: Remove CONFIG_NR_CPUS configuration

On Fri, Jan 24, 2025 at 12:41:38PM +0100, Uladzislau Rezki wrote:
> On Thu, Jan 23, 2025 at 12:29:45PM -0800, Paul E. McKenney wrote:
> > On Thu, Jan 23, 2025 at 07:58:26PM +0100, Uladzislau Rezki (Sony) wrote:
> > > This configuration specifies the maximum number of CPUs which
> > > is set to 8. The problem is that it can not be overwritten for
> > > something higher.
> > > 
> > > Remove that configuration for TREE05, so it is possible to run
> > > the torture test on as many CPUs as many system has.
> > > 
> > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> > 
> > You should be able to override this on the kvm.sh command line by
> > specifying "--kconfig CONFIG_NR_CPUS=128" or whatever number you wish.
> > For example, see the torture.sh querying the system's number of CPUs
> > and then specifying it to a number of tests.
> > 
> > Or am I missing something here?
> > 
> It took me a while to understand what happens. Apparently there is this
> 8 CPUs limitation. Yes, i can do it manually by passing --kconfig but
> you need to know about that. I have not expected that.
> 
> Therefore i removed it from the configuration because i have not found
> a good explanation why we need. It is confusing instead :)

Right now, if I do a run with --configs "TREE10 14*CFLIST", this will
make use of 20 systems with 80 CPUs each.  If you remove that line from
TREE05, won't each instance of TREE05 consume a full system, for a total
of 33 systems?  Yes, I could use "--kconfig CONFIG_NR_CPUS=8" on the
command line, but that would affect all the scenarios, not just TREE05.
Including (say) TINY01, where I believe that it would cause kvm.sh
to complain about a Kconfig conflict.

Hence me not being in favor of this change.  ;-)

Is there another way to make things work for both situations?

							Thanx, Paul