commit 6b9c2603ce07f70de9c7a8d335ecd028e8ff11f3
author Paul Jackson <pj@sgi.com> Sun Jan 08 01:02:02 2006 -0800
committer Linus Torvalds <torvalds@g5.osdl.org> Sun Jan 08 20:13:45 2006 -0800
tree 38b009da71a1f93bbda8621c7d2721c18913260d
parent c417f0242ebe578924a30d4e53d35b5059fed4e7

[PATCH] cpuset: use rcu directly optimization

Optimize the cpuset impact on page allocation, the most performance critical
cpuset hook in the kernel.

On each page allocation, the cpuset hook needs to check for a possible change
in the current tasks cpuset.  It can now handle the common case, of no change,
without taking any spinlock or semaphore, thanks to RCU.

Convert a spinlock on the current task to an rcu_read_lock(), saving
approximately a memory barrier and an atomic op, depending on architecture.

This is done by adding rcu_assign_pointer() and synchronize_rcu() calls to the
write side of the task->cpuset pointer, in cpuset.c:attach_task(), to delay
freeing up a detached cpuset until after any critical sections referencing
that pointer.

Thanks to Andi Kleen, Nick Piggin and Eric Dumazet for ideas.

Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>