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

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Message-ID: <1317224038.24040.52.camel@twins>
Date:	Wed, 28 Sep 2011 17:33:58 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.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 12:29 -0300, Glauber Costa wrote:
> On 09/28/2011 09:53 AM, Peter Zijlstra wrote:
> > 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.
> >
> Well, I think x86-32 is unlikely to ever really go away.

Sadly I'd agree with you, but that's not really the point, the only 32
bit arch that has !32 bit cputime_t is s390.

But yeah, death to ia32 (and everything else 32bit fwiw)!
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