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* [patch 0/8] Allow inlined spinlocks again V5
@ 2009-08-29 10:21 Heiko Carstens
  2009-08-29 10:21 ` Heiko Carstens
                   ` (9 more replies)
  0 siblings, 10 replies; 24+ messages in thread
From: Heiko Carstens @ 2009-08-29 10:21 UTC (permalink / raw)
  To: Andrew Morton, Ingo Molnar, Linus Torvalds, David Miller,
	Benjamin Herrenschmidt <be>
  Cc: linux-arch, Peter Zijlstra, Arnd Bergmann, Nick Piggin,
	Martin Schwidefsky, Horst Hartmann, Christian Ehrhardt,
	Heiko Carstens

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.

^ permalink raw reply	[flat|nested] 24+ messages in thread

end of thread, other threads:[~2009-09-01 13:20 UTC | newest]

Thread overview: 24+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2009-08-29 10:21 [patch 0/8] Allow inlined spinlocks again V5 Heiko Carstens
2009-08-29 10:21 ` Heiko Carstens
2009-08-29 10:21 ` [patch 1/8] powerpc: rename __spin_try_lock() and friends Heiko Carstens
2009-08-29 10:21   ` Heiko Carstens
2009-08-29 10:21 ` [patch 2/8] sparc: " Heiko Carstens
2009-08-29 10:21   ` Heiko Carstens
2009-08-29 22:27   ` David Miller
2009-08-29 10:21 ` [patch 3/8] m68k/asm-offsets: rename pt_regs offset defines Heiko Carstens
2009-08-29 10:21   ` Heiko Carstens
2009-08-29 10:21 ` [patch 4/8] m68k/asm-offsets: rename signal defines Heiko Carstens
2009-08-29 10:21   ` Heiko Carstens
2009-08-29 10:21 ` [patch 5/8] m68k: calculate thread_info offset with asm offset Heiko Carstens
2009-08-29 10:21   ` Heiko Carstens
2009-08-29 10:21 ` [patch 6/8] spinlock: move spinlock function bodies to header file Heiko Carstens
2009-08-29 10:21   ` Heiko Carstens
2009-08-29 10:21 ` [patch 7/8] spinlock: allow inlined spinlocks Heiko Carstens
2009-08-29 10:21   ` Heiko Carstens
2009-08-29 10:21 ` [patch 8/8] spinlock: inline code for all locking variants on s390 Heiko Carstens
2009-08-29 10:21   ` Heiko Carstens
2009-08-29 11:16 ` [patch 0/8] Allow inlined spinlocks again V5 Ingo Molnar
2009-08-29 13:59   ` Heiko Carstens
2009-08-29 14:13     ` Ingo Molnar
2009-08-31  8:59       ` Heiko Carstens
2009-09-01 13:19         ` Ingo Molnar

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