[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <e27ec83e-ab0c-4b46-b01d-4d1a5dd43b64@paulmck-laptop>
Date: Mon, 17 Jul 2023 11:16:46 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-team@...a.com, rostedt@...dmis.org,
atthias Brugger <matthias.bgg@...il.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Michał Mirosław <mirq-linux@...e.qmqm.pl>,
Dmitry Osipenko <dmitry.osipenko@...labora.com>,
Sachin Sant <sachinp@...ux.ibm.com>,
Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH rcu 3/6] srcu,notifier: Remove #ifdefs in favor of SRCU
Tiny srcu_usage
On Mon, Jul 17, 2023 at 11:09:56AM -0700, Linus Torvalds wrote:
> On Mon, 17 Jul 2023 at 11:03, Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > +// Dummy structure for srcu_notifier_head.
> > +struct srcu_usage {
> > + char srcuu_dummy;
> > +};
> > +
> > +#define __SRCU_USAGE_INIT(name) { .srcuu_dummy = 0, }
>
> You really should be able to just do
>
> struct srcu_usage { };
> #define __SRCU_USAGE_INIT(name) { }
>
> which is something we've done for ages for spinlocks in
>
> include/linux/spinlock_types_up.h
>
> because while we had a gcc bug wrt empty structures, that was ages ago
> (ie "gcc-2.x").
>
> See commit a1365647022e ("[PATCH] remove gcc-2 checks") from 2006.
>
> So we've already had these kinds of empty dummy structs for literally
> over a decade in active use. Exactly so that you can avoid having to
> use #ifdef's etc, and can just always assume you have a spinlock, even
> if it doesn't generate any code or any data overhead.
Showing my age again, I guess. ;-)
Thank you for the hint! I will rework this as you suggest.
Thanx, Paul
Powered by blists - more mailing lists