[patch 0/8] Allow inlined spinlocks again V5

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

This patch set allows to have inlined spinlocks again.

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.

V4: allow architectures to specify for each lock/unlock variant if
    it should be kept out-of-line or inlined.

V5: simplify ifdefs as pointed out by Linus. Fix architecture compile
    breakages caused by this change.

Linus, Ingo, do you still have objections?

---

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.
By default all locking code remains out-of-line. An architecture can
specify

#define __spin_lock_is_small

in arch/<whatever>/include/asm/spinlock.h to force inlining of a locking
function.

defconfig cross compile tested for alpha, arm, x86, x86_64, ia64, m68k,
m68knommu, mips, powerpc, powerpc64, sparc64, s390, s390x.