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

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Date:	Fri, 6 Jan 2012 18:30:19 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	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, Jan 06, 2012 at 08:58:55AM -0800, Linus Torvalds 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?
> 
>    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.
> 
>  - 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.
> 
> 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.
> 
> It may have been wrong before too, but at least on 64-bit
> architectures it didn't really matter. Now the sparse fixes have made
> "cputime64_t" a separate type that will complain about casting, so it
> not only casts the type to a (potentially different and wrong size),
> but it also breaks the sparse checks.
> 
> I tried to fix up the ones that caused actual conflicts (due to
> changes nearby, like the ones in asm-generic), but the ones that
> didn't actually cause conflicts (powerpc and s390) I left alone.
> 
> Guys, can you take a look? Also double-check my resolve of the
> set_cpu_sd_state_idle() call in kernel/time/tick-sched.c, please. I've
> pushed it out, and it seems to work for me, but...

Yes looks good. We want it to be called from idle loop entry but not
from idle interrupts. So moving it to tick_nohz_idle_enter() is the
right thing.
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