linux-kernel - Re: [PATCH 1/1] rcu/rcuscale: Stop kfree_scale_thread thread(s) after unloading rcuscale

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Date:   Thu, 16 Mar 2023 10:50:53 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] rcu/rcuscale: Stop kfree_scale_thread thread(s)
 after unloading rcuscale

On Thu, Mar 16, 2023 at 10:57:06AM -0400, Joel Fernandes wrote:
> On Thu, Mar 16, 2023 at 9:53 AM Zhuo, Qiuxu <qiuxu.zhuo@...el.com> wrote:
> >
> [...]
> > > >> From: Paul E. McKenney <paulmck@...nel.org> [...]
> > > >>>>
> > > >>>> How about to pull the rcu_scale_cleanup() function after
> > > >> kfree_scale_cleanup().
> > > >>>> This groups kfree_* functions and groups rcu_scale_* functions.
> > > >>>> Then the code would look cleaner.
> > > >>>> So, do you think the changes below are better?
> > > >>>
> > > >>> IMHO, I don't think doing such a code move is better. Just add a new
> > > >>> header file and declare the function there. But see what Paul says
> > > >>> first.
> > > >>
> > > >> This situation is likely to be an early hint that the kvfree_rcu()
> > > >> testing should be split out from kernel/rcu/rcuscale.c.
> > > >
> > > > Another is that it's a bit expensive to create a new header file just
> > > > for eliminating a function declaration. ;-)
> > >
> > > What is so expensive about new files? It is a natural organization structure.
> > >
> > > > So, if no objections, I'd like to send out the v2 patch with the updates below:
> > > >
> > > >   - Move rcu_scale_cleanup() after kfree_scale_cleanup() to eliminate the
> > > >     declaration of kfree_scale_cleanup(). Though this makes the patch bigger,
> > > >     get the file rcuscale.c much cleaner.
> > > >
> > > >   - Remove the unnecessary step "modprobe torture" from the commit
> > > message.
> > > >
> > > >   - Add the description for why move rcu_scale_cleanup() after
> > > >     kfree_scale_cleanup() to the commit message.
> > >
> > > Honestly if you are moving so many lines around, you may as well split it out
> > > into a new module.
> > > The kfree stuff being clubbed in the same file has also been a major
> > > annoyance.
> >
> > I'm OK with creating a new kernel module for these kfree stuffs,
> > but do we really need to do that?

It is not a particularly high priority.

> If it were me doing this, I would try to split it just because in the
> long term I may have to maintain or deal with it.
> 
> I was also thinking a new scale directory _may_ make sense for
> performance tests.
> 
> kernel/rcu/scaletests/kfree.c
> kernel/rcu/scaletests/core.c
> kernel/rcu/scaletests/ref.c
> 
> Or something like that.

I don't believe we are there yet, but...

> and then maybe putt common code into: kernel/rcu/scaletests/common.c

...splitting out the common code within the current directory/file
structure makes a lot of sense to me.  Not that I have checked up on
exactly how much common code there really is.  ;-)

							Thanx, Paul

>  - Joel
> 
> >
> > @paulmck, what's your suggestion for the next step?
> >
> > >  - Joel
> > >
> > >
> > > > Thanks!
> > > > -Qiuxu
> > > >
> > > >> [...]