linux-kernel - Re: linux-next: tip tree build warnings

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Message-ID: <20090907105928.2646cb11@skybase>
Date:	Mon, 7 Sep 2009 10:59:28 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Subject: Re: linux-next: tip tree build warnings

On Thu, 3 Sep 2009 14:13:26 +0200
Heiko Carstens <heiko.carstens@...ibm.com> wrote:

> On Thu, Sep 03, 2009 at 10:38:44AM +0200, Ingo Molnar wrote:
> > * Stephen Rothwell <sfr@...b.auug.org.au> wrote:
> > > cputime_t is variously "u64", "unsigned long long" and "unsigned 
> > > long" on different architectures.
> > 
> > Should be unsigned long i think. Most architectures use it as 
> > unsigned long via include/asm-generic/cputime.h, except these three:
> > 
> >  arch/ia64/include/asm/cputime.h:typedef u64 cputime_t;
> >  arch/powerpc/include/asm/cputime.h:typedef u64 cputime_t;
> >  arch/s390/include/asm/cputime.h:typedef unsigned long long cputime_t;
> > 
> > Or we could eliminate the type altogether as well and standardize on 
> > u64. Thomas?
> 
> s390 uses 64 bit cputime_t because we want the high resolution also in
> 32 bit kernels. So standardizing on u64 would be the preferred solution
> for us.

The cputime_t type serves/served two purposes: 1) make it clear that
this is NOT a jiffie value, it is an architecture defined type with
architecture dependent semantic, 2) by redefining cputime_t to a
structure with a single embedded unsigned long I have been able to
identify all places in the kernel that do not use the proper cputime
functions. I'm not sure if we need 2) anymore.

-- 
blue skies,
   Martin.

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

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