IPC lock patch performance improvement

[Duc Vianney <dvianney@us.ibm.com>]

I ran the LMbench Pipe and IPC latency test bucket against the IPC lock
patch from Mingming Cao and found the patch improves the performance of
those functions from 1% to 9%. See the attached data. The kernel under
test is 2.5.29, SMP kernel running on a 4-way 500 MHz. The data for
2.5.29s4-ipc represents the average of three runs.

                                                           Percent
                                  2.5.29s4 2.5.29s4-ipc Improvement
Pipe latency                         12.51     11.43         9%
AF_Unix sock stream latency          21.61     19.82         8%
UDP latency using localhost          36.28     35.12         3%
TCP latency using localhost          56.90     54.89         4%
RPC/tcp latency using local host    123.30    121.91         1%
RPC/udp latency using localhost      89.78     88.70         1%
TCP/IP connection cost to localhost 192.74    187.76         3%
Note: Latency is in microseconds
Note: 2.5.29s4 is the base 2.5.29 SMP kernel running on a 4-way,
2.5.29s4-ipc is the base 2.5.29 SMP kernel built with IPC lock patch.

Duc. dvianney@us.ibm.com