linux-kernel - Re: [GIT PULL] scheduler changes for v3.3

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Date:	Sat, 7 Jan 2012 19:43:48 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andreas Schwab <schwab@...ux-m68k.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] scheduler changes for v3.3

On Fri, 6 Jan 2012 08:58:55 -0800
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Thu, Jan 5, 2012 at 6:08 AM, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > Please pull the latest sched-core-for-linus git tree from:
> >
> >   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-core-for-linus
> 
> Ugh. So I got conflicts on this one.  Big deal, fix them up.
> 
> But as I was fixing them up, I hit two problems that I wanted people
> to take a look at:
> 
>  - some of the code was utter crap. Look at my fixup for
> include/asm-generic/cputime.h, for example. Notice how I had to change
> __msecs to __usec, and notice the bogus semicolons that I removed?

Yes, the semicolons had been crap and the parameter name suboptimal.

>    This came in through commit 648616343cdb ("[S390] cputime: add
> sparse checking and cleanup") which is also mis-named: it's not
> S390-specific. Martin, please take a look.

Yeah, I had that patch in the s390 tree before it got moved to a tip tree.
I tend to tag everything in my tree with [S390].
 
>  - I did not do the right thing for the "usecs_to_cputime64()" fixup.
> Please take a look at commit 34845636a184 ("procfs: do not confuse
> jiffies with cputime64_t") which introduced that "usecs_to_cputime64()
> thing, and which clashes badly with the sparse cleanups.

There had been some fallout from the two changes.
 
> And by "clashes badly", I mean it. The sparse cleanups added a lot of
> casts between the types, which means that the mindless
> 
>     +#define usecs_to_cputime64(us)         usecs_to_cputime(us)
> 
> introduced by that commit 34845636a184 is now likely *wrong*, because
> "usecs_to_cputime()" now explicitly casts to a non-64-bit cputime_t.

Surprisingly sparse does not give a warning if the base type of two
__nowarn types is the same. All three VIRT_CPU_ACCOUNTING architectures
use u64 or unsigned long long for cputime_t and cputime64_t. It does
work but I agree that an explicit cast to cputime64_t would be better.

-- 
blue skies,
   Martin.

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

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