diff options
author | Christoph Lameter <clameter@sgi.com> | 2008-01-08 02:20:30 -0500 |
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committer | Christoph Lameter <christoph@stapp.engr.sgi.com> | 2008-02-07 20:47:41 -0500 |
commit | 1f84260c8ce3b1ce26d4c1d6dedc2f33a3a29c0c (patch) | |
tree | d57e305168291f1b0f5f2d42853d2c2419f4140b /include/linux/slub_def.h | |
parent | 683d0baad3d6e18134927f8c28ee804dbe10fe71 (diff) |
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 <clameter@sgi.com>
Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'include/linux/slub_def.h')
0 files changed, 0 insertions, 0 deletions