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

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Message-ID: <Z5PMGlDb489VEZ7S@pc636>
Date: Fri, 24 Jan 2025 18:21:30 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Uladzislau Rezki <urezki@...il.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 2/4] torture: Remove CONFIG_NR_CPUS configuration

On Fri, Jan 24, 2025 at 07:45:23AM -0800, Paul E. McKenney wrote:
> 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?
> 
OK, i see. Well. I will just go with --kconfig CONFIG_NR_CPUS=foo if i
need more CPUs for TREE05.

I will not resist, we just drop this patch :)

--
Uladzislau Rezki