linux-kernel - Re: [PATCH] rcu/performance: Fix kfree_perf_init() build warning on 32-bit kernels

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Message-ID: <20200603181109.GA5438@paulmck-ThinkPad-P72>
Date:   Wed, 3 Jun 2020 11:11:09 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        linux-tip-commits@...r.kernel.org, x86 <x86@...nel.org>
Subject: Re: [PATCH] rcu/performance: Fix kfree_perf_init() build warning on
 32-bit kernels

On Tue, May 26, 2020 at 09:14:13PM -0400, Joel Fernandes wrote:
> On Tue, May 26, 2020 at 08:27:44PM +0200, Ingo Molnar wrote:
> [...]
> > ./include/linux/kern_levels.h:5:18: warning: format ‘%lu’ expects argument
> > of type ‘long unsigned int’, but argument 2 has type ‘unsigned int’
> > [-Wformat=] 5 | #define KERN_SOH "\001"  /* ASCII Start Of Header */ |
> > ^~~~~~
> > ./include/linux/kern_levels.h:9:20: note: in expansion of macro ‘KERN_SOH’
> >     9 | #define KERN_ALERT KERN_SOH "1" /* action must be taken immediately */
> >       |                    ^~~~~~~~
> > ./include/linux/printk.h:295:9: note: in expansion of macro ‘KERN_ALERT’
> >   295 |  printk(KERN_ALERT pr_fmt(fmt), ##__VA_ARGS__)
> >       |         ^~~~~~~~~~
> > kernel/rcu/rcuperf.c:726:2: note: in expansion of macro ‘pr_alert’
> >   726 |  pr_alert("kfree object size=%lu\n", kfree_mult * sizeof(struct kfree_obj));
> >       |  ^~~~~~~~
> > kernel/rcu/rcuperf.c:726:32: note: format string is defined here
> >   726 |  pr_alert("kfree object size=%lu\n", kfree_mult * sizeof(struct kfree_obj));
> >       |                              ~~^
> >       |                                |
> >       |                                long unsigned int
> >       |                              %u
> > 
> > 
> > The reason for the warning is that both kfree_mult and sizeof() are 
> > 'int' types on 32-bit kernels, while the format string expects a long.
> > 
> > Instead of casting the type to long or tweaking the format string, the 
> > most straightforward solution is to upgrade kfree_mult to a long. 
> > Since this depends on CONFIG_RCU_PERF_TEST
> 
> Thanks for fixing it.
> 
> > BTW., could we please also rename this code from 'PERF_TEST'/'perf test'
> > to 'PERFORMANCE_TEST'/'performance test'? At first glance I always
> > mistakenly believe that it's somehow related to perf, while it isn't. =B-)
> 
> Would it be better to call it 'RCUPERF_TEST' instead of the
> 'RCU_PERFORMANCE_TEST' you are proposing? I feel the word 'PERFORMANCE' is
> too long.  Also, 'rcuperf test' instead of the 'rcu performance test' you are
> proposing.  I am Ok with doing it however you and Paul want it though, let me
> know.

As long as we are bikeshedding the name...  How about refscale.c and
RCU_REF_SCALE_TEST on the one hand and rcuscale.c and RCU_SCALE_TEST on
the other?  That keeps the names reasonably short and does not allude
to perf at all.

> Paul, should I send you a renaming patch for the new performance tests as
> well (which I believe should be in the -dev branch).

I am still modifying refperf/refscale/refwhatever, so I will update
that one.

						Thanx, Paul