From mboxrd@z Thu Jan  1 00:00:00 1970
From: Heiko Carstens <heiko.carstens@de.ibm.com>
Subject: Re: [patch 2/3] spinlock: allow inlined spinlocks
Date: Sun, 16 Aug 2009 23:33:43 +0200
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To: Ingo Molnar <mingo@elte.hu>
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>

On Sun, Aug 16, 2009 at 10:48:31PM +0200, Ingo Molnar wrote:
> * 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?

What I tried to say: in general we want to have all locking functions inlined.
This is because all our measurements show if anything gets inlined performance
improves. This is even true for large functions.

> 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.

All measurements were done with CONFIG_PREEMPT off.