linux-kernel - Re: Linux 3.1-rc9

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Message-ID: <20111017095544.6bf76dea@de.ibm.com>
Date:	Mon, 17 Oct 2011 09:55:44 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Simon Kirby <sim@...tway.ca>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: Linux 3.1-rc9

On Sun, 16 Oct 2011 18:39:57 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> That stupid definition of cputime_add() has apparently existed as-is
> since it was introduced in 2005. Why do we have code like this:
> 
>     times->utime = cputime_add(times->utime, t->utime);
> 
> instead of just
> 
>     times->utime += t->utime;
> 
> which seems not just shorter, but more readable too? The reason is not
> some type safety in the cputime_add() thing, it's just a macro.
> 
> Added Martin and Ingo to the discussion - Martin because he added that
> cputime_add in the first place, and Ingo because he gets the most hits
> on kernel/sched_stats.h. Guys - you can see the history on lkml.

I introduced those macros to find all the places in the kernel operating
on a cputime value. The additional debug patch defined cputime_t as a
struct which contained a single u64. That way I got a compiler error
for every place I missed.

The reason for the cputime_xxx primitives has been my fear that people
ignore the cputime_t type and just use unsigned long (as they always
have). That would break s390 which needs a u64 for its cputime value.
Dunno if we still need it, seems like we got used to using cputime_t.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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