linux-kernel - Re: [RFD 4/9] Make total

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Message-ID: <20110928101357.5a90c2ab@de.ibm.com>
Date:	Wed, 28 Sep 2011 10:13:57 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Glauber Costa <glommer@...allels.com>,
	linux-kernel@...r.kernel.org, paul@...lmenage.org,
	lizf@...fujitsu.com, daniel.lezcano@...e.fr,
	jbottomley@...allels.com,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [RFD 4/9] Make total_forks per-cgroup

On Wed, 28 Sep 2011 00:00:37 +0200
Peter Zijlstra <a.p.zijlstra@...llo.nl> 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.

-- 
blue skies,
   Martin.

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

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