Hi Andrew,

Here is the updated ipc lock patch:

- It greatly reduces the lock contention by having one lock per id. The
global spinlock is removed and a spinlock is added in kern_ipc_perm
structure.

- Uses ReadCopyUpdate in grow_ary() for locking-free resizing.

- In the places where ipc_rmid() is called, delay calling ipc_free() to
RCU callbacks.  This is to prevent ipc_lock() returning an invalid
pointer after ipc_rmid().  In addition, use the workqueue to enable RCU
freeing vmalloced entries.

Also some other changes:
- Remove redundant ipc_lockall/ipc_unlockall
- Now ipc_unlock() directly takes IPC ID pointer as argument, avoid
extra looking up the array.

The changes are made based on the input from Huge Dickens, Manfred
Spraul and Dipankar Sarma. In addition, Cliff White has run OSDL's dbt1
test on a 2 way against the earlier version of this patch. Results shows
about 2-6% improvement on the average number of transactions per
second.  Here is the summary of his tests:

                        2.5.42-mm2      2.5.42-mm2-ipclock
----------------------------------------------------------
Average over 5 runs	85.0 BT		89.8 BT
Std Deviation 5 runs	7.4  BT		1.0 BT

Average over 4 best 	88.15 BT	90.2 BT
Std Deviation 4 best	2.8 BT		0.5 BT

Full details of the tests could be found here:
http://www.osdl.org/projects/dbt1prfrns/results/mingming/index.html

patch is against 2.5.44-mm4.  Please include or give any feedback.

Thanks,

Mingming Cao