[patch 0/3] Allow inlined spinlocks again V3

[Heiko Carstens <heiko.carstens@de.ibm.com>]

Hi Andrew,

since there were no objections to this patch set, would you mind picking
it up for -mm? The patches are against current Linus' git head but also
apply on top of the latest mmotm patch set.

===

This patch set allows to have inlined spinlocks again.

The rationale behind this is that function calls on at least s390 are
expensive.

If one considers that server kernels are usually compiled with
!CONFIG_PREEMPT a simple spin_lock is just a compare and swap loop.
The extra overhead for a function call is significant.
With inlined spinlocks overall cpu usage gets reduced by 1%-5% on s390.
These numbers were taken with some network benchmarks. However I expect
any workload that calls frequently into the kernel and which grabs a few
locks to perform better.

The implementation is straight forward: move the function bodies of the
locking functions to static inline functions and place them in a header
file.
Dependent on CONFIG_SPINLOCK_INLINE generate out-of-line or inlined
locking functions.

The patches should be self explaining.

V2: rewritten from scratch - now also with readable code

V3: removed macro to generate out-of-line spinlock variants since that
    would break ctags. As requested by Arnd Bergmann.