Re: [RFD 4/9] Make total_forks per-cgroup

[Glauber Costa]

On 09/28/2011 05:13 AM, Martin Schwidefsky wrote:
> On Wed, 28 Sep 2011 00:00:37 +0200
> Peter Zijlstra<a.p.zijlstra@xxxxxxxxx>  wrote:
>
> > On Fri, 2011-09-23 at 19:20 -0300, Glauber Costa wrote:
> > > @@ -1039,6 +1035,8 @@ static void posix_cpu_timers_init(struct task_struct *tsk)
> > >          INIT_LIST_HEAD(&tsk->cpu_timers[2]);
> > >   }
> > >
> > > +struct task_group *task_group(struct task_struct *p);
> >
> > That doesn't appear to be actually used in this file..
> >
> > Also, since there's already a for_each_possible_cpu() loop in that
> > proc/stat function, would it yield some code improvement to make
> > total_forks a cpu_usage_stat?
> >
> > I guess the whole cputime64_t crap gets in the way of that being
> > natural...
> >
> > We could of course kill off the cputime64_t thing, its pretty pointless
> > and its a u64 all over the board. I think Martin or Heiko created this
> > stuff (although I might be wrong, my git tree doesn't go back that far).
>
> The reason to introduce cputime_t has been that different architecture
> needed differently sized integers for their respective representation
> of cputime. On x86-32 the number of ticks is recorded in a u32, on s390
> we needed a u64 for the cpu timer values. cputime64_t is needed for
> cpustat and other sums of cputime that would overflow a cputime_t
> (in particular on x86-32 with the u32 cputime_t and the u64 cputime64_t).
>
> Now we would convert everything to u64 but that would cause x86-32 to
> use 64-bit arithmetic for the tick counter. If that is acceptable I
> can't say.
If we get rid of cputime64_t, it doesn't mean we need to get rid of 
cputime_t. Or am I missing the point here?

We would still have to call an analogous of cputime_to_cputime64 before 
using it, but I get that where it matters, gcc can even make it void.
And for all the rest, we do u64 math and typing and just get happy.

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