From 1f84260c8ce3b1ce26d4c1d6dedc2f33a3a29c0c Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Mon, 7 Jan 2008 23:20:30 -0800 Subject: SLUB: Alternate fast paths using cmpxchg_local Provide an alternate implementation of the SLUB fast paths for alloc and free using cmpxchg_local. The cmpxchg_local fast path is selected for arches that have CONFIG_FAST_CMPXCHG_LOCAL set. An arch should only set CONFIG_FAST_CMPXCHG_LOCAL if the cmpxchg_local is faster than an interrupt enable/disable sequence. This is known to be true for both x86 platforms so set FAST_CMPXCHG_LOCAL for both arches. Currently another requirement for the fastpath is that the kernel is compiled without preemption. The restriction will go away with the introduction of a new per cpu allocator and new per cpu operations. The advantages of a cmpxchg_local based fast path are: 1. Potentially lower cycle count (30%-60% faster) 2. There is no need to disable and enable interrupts on the fast path. Currently interrupts have to be disabled and enabled on every slab operation. This is likely avoiding a significant percentage of interrupt off / on sequences in the kernel. 3. The disposal of freed slabs can occur with interrupts enabled. The alternate path is realized using #ifdef's. Several attempts to do the same with macros and inline functions resulted in a mess (in particular due to the strange way that local_interrupt_save() handles its argument and due to the need to define macros/functions that sometimes disable interrupts and sometimes do something else). [clameter: Stripped preempt bits and disabled fastpath if preempt is enabled] Signed-off-by: Christoph Lameter Reviewed-by: Pekka Enberg Cc: Signed-off-by: Andrew Morton --- arch/x86/Kconfig | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch') diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index c95482b6b6dd..9d0acedf5f3f 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -52,6 +52,10 @@ config HAVE_LATENCYTOP_SUPPORT config SEMAPHORE_SLEEPERS def_bool y +config FAST_CMPXCHG_LOCAL + bool + default y + config MMU def_bool y -- cgit v1.2.1