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Date:   Wed, 13 Feb 2019 15:56:46 +0100
From:   Frederic Weisbecker <frederic@kernel.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Mauro Carvalho Chehab <mchehab@s-opensource.com>,
        "David S . Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Pavan Kondeti <pkondeti@codeaurora.org>,
        Ingo Molnar <mingo@kernel.org>,
        Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [PATCH 02/32] locking/lockdep: Introduce struct lock_usage
Message-ID: <20190213145645.GC8524@lenoir>
References: <20190212171423.8308-1-frederic@kernel.org>
 <20190212171423.8308-3-frederic@kernel.org>
 <CAHk-=witwrbw0mExDpGzxYic87FpGhe1gCB+nqm1woUvwPY9GA@mail.gmail.com>
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On Tue, Feb 12, 2019 at 09:38:42AM -0800, Linus Torvalds wrote:
> On Tue, Feb 12, 2019 at 9:14 AM Frederic Weisbecker <frederic@kernel.org> wrote:
> >
> > +static u64 lock_usage_mask(struct lock_usage *usage)
> > +{
> > +       return BIT(usage->bit);
> > +}
> 
> More insane "u64" - and it's *incorrect* too.
> 
>     #define BIT(nr)                    (1UL << (nr))
> 
> fundamentally means that "BIT()" can only work on up to "unsigned long".
> 
> So this odd use of u64 seems to be a disease. It only uses more memory
> (and more CPU) for no obvious reason.
> 
> u64 is not some "default type". It's expensive and shouldn't be used
> unless you have a *reason* for it.

Right, I'll simply move "[PATCH 03/32] locking/lockdep: Convert usage_mask to u64"
at the first position and follow up on that to justify its use.

Thanks.