Re: Linux 3.1-rc9

[Martin Schwidefsky <schwidefsky@de.ibm.com>]

On Sun, 16 Oct 2011 18:39:57 -0700
Linus Torvalds <torvalds@linux-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.