From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch 2/3] spinlock: allow inlined spinlocks
Date: Sun, 16 Aug 2009 22:48:31 +0200
Message-ID: <20090816204831.GA23773@elte.hu>
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To: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>, Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-arch@vger.kernel.org, Martin Schwidefsky <schwidefsky@de.ibm.com>, Arnd Bergmann <arnd@arndb.de>, Horst Hartmann <horsth@linux.vnet.ibm.com>, Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>, Nick Piggin <nickpiggin@yahoo.com.au>


* Heiko Carstens <heiko.carstens@de.ibm.com> wrote:

> On Sun, Aug 16, 2009 at 08:06:31PM +0200, Ingo Molnar wrote:
> > * Heiko Carstens <heiko.carstens@de.ibm.com> wrote:
> > > > #define __spin_lock_is_small
> > 
> > > > +unsigned long __lockfunc _spin_lock_irqsave_nested(spinlock_t *lock, int subclass)
> > > > +							__acquires(lock);
> > > > +
> > > > +#ifdef __spin_lock_is_small
> > > > +#define _spin_lock(lock) __spin_lock(lock)
> > > > +#else
> > > > +void __lockfunc _spin_lock(spinlock_t *lock)		__acquires(lock);
> > > > +#endif
> > 
> > Dunno - i'm somewhat wary of introducing a 2^28 variability here. 
> > (although the number of real variations is much lower - but still).
> > 
> > What's the current situation on s390, precisely which of the 28 lock 
> > functions are a win to be inlined and which ones are a loss? Do you 
> > have a list/table perhaps?
> 
> No list unfortunately. [...]

Well, if you dont know the functions you want to inline, how will 
you make intelligent use of this facility then in s390?

Btw., i just noticed that s390 has CONFIG_PREEMPT turned on by 
default in its defconfig. Have you made your measurements with 
CONFIG_PREEMPT? If yes then the current inlining rules in spinlock.h 
will turn all the locking APIs into functions.

Could you perhaps re-try your measurements with CONFIG_PREEMPT 
turned off? I suspect you'll see different behavior.

	Ingo