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

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Date:	Wed, 28 Sep 2011 14:53:38 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
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, 2011-09-28 at 14:42 +0200, Martin Schwidefsky wrote:

> > That is, am I missing some added value of all this cputime*() foo?
> 
> C can do the math as long as the encoding of the cputime is simple enough.
> Can we demand that a cputime value needs to be an integral type ?

I'd like to think we can ;-)

> What I did when I wrote all that stuff is to define cputime_t as a struct
> that contains a single u64. That way I found all the places in the kernel
> that used a cputime and could convert the code accordingly.

Indeed, that makes it a non-simple type and breaks all the C arith bits.

> My fear is that if the cputime_xxx operations are removed, code will
> sneak in again that just uses an unsigned long instead of a cputime_t.
> That would break any arch that requires something bigger than a u32 for
> its cputime.

Which is only a problem for 32bit archs, of which s390 is the only one
that matters, right? Hurm,. could we do something with sparse? Lots of
people run sparse.

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