Timing of the devmtx contention patch using three scenarios:

1: open/read/close and a open/write/close in a loop
2: read and write in a loop
3: open/read/close


Profileng of scenario #1 shows this:
$ ministat -w 72 devmtx1.r210851.20100805092611.log devmtx1.r210851M.20100805103753.log
x devmtx1.r210851.20100805092611.log
+ devmtx1.r210851M.20100805103753.log
+------------------------------------------------------------------------+
|    +                                                                x  |
|+  ++ +                                                             xxxx|
| |_AM_|                                                             |MA||
+------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x   5         74.54         75.22         74.89        74.926    0.25938389
+   5         60.93         62.15         61.73          61.6     0.4501111
Difference at 95.0% confidence
        -13.326 +/- 0.535747
        -17.7855% +/- 0.715035%
        (Student's t, pooled s = 0.367342)

Profileng of scenario #2 shows this:
$ ministat -w 72 devmtx2.r210851.20100805092611.log devmtx2.r210851M.20100805103753.log
x devmtx2.r210851.20100805092611.log
+ devmtx2.r210851M.20100805103753.log
+------------------------------------------------------------------------+
|+                                                                      x|
|+                                                                      x|
|+                                                                      x|
|+                                                                      x|
|+                                                                      x|
|A                                                                      A|
+------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x   5         64.97         65.31         65.01        65.062    0.14131525
+   5          9.75          9.97          9.82          9.84   0.087464278
Difference at 95.0% confidence
        -55.222 +/- 0.17139
        -84.876% +/- 0.263426%
        (Student's t, pooled s = 0.117516)

Profileng of scenario #3 shows this:
$ ministat -w 72 devmtx3.r210851.20100805092611.log devmtx3.r210851M.20100805103753.log
x devmtx3.r210851.20100805092611.log
+ devmtx3.r210851M.20100805103753.log
+------------------------------------------------------------------------+
|+ +                                                              x      |
|+ +  +                                                           x  xx x|
||_A_|                                                            |__A_| |
+------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x   5         73.27         75.57          74.5         74.32     0.9681942
+   5         49.19         51.03         49.82        49.816    0.75145193
Difference at 95.0% confidence
        -24.504 +/- 1.26392
        -32.9709% +/- 1.70065%
        (Student's t, pooled s = 0.866626)
$