status performance and ... chdir

[Matthew D. Fuller]

On Wed, Sep 10, 2008 at 03:52:11PM +1000 I heard the voice of
Robert Collins, and lo! it spake thus:
> 
> Here are four timing runs, reading the contents of a mozilla tree:

And here are ministat results of 10 data points of each version of
readdir.  Running over my ~/mail, which turned up Count: 412 (out of
143,185 lines that find gives).  Raw data files attached.  All times in
ms.  This is on a ~10 month old FreeBSD 7.x, so that gives us a good
platform spread.


First, the wall times (note that these are to 10ms precision):

x wall.chdir
+ wall.nochdir
+-------------------------------------------------------------------------+
| x                                                               +       |
| xx                                                              ++      |
| xx                                                             +++      |
|xxxx                                                            +++     +|
| A|                                                                      |
|                                                                |MA_|    |
+-------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x  10          1850          1880          1860          1864     8.4327404
+  10          2490          2570          2500          2508     22.997584
Difference at 95.0% confidence
        644 +/- 16.2743
        34.5494% +/- 0.873083%
        (Student's t, pooled s = 17.3205)



User:

x user.chdir
+ user.nochdir
+-------------------------------------------------------------------------+
|                           +                  x                          |
|*        x                 ++      x+x        x+ x  + +xx     x+        +|
|                   |____________________A_____M_____________|            |
|                   |_____________________A____________________|          |
+-------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x  10            77           597           466         409.7     170.38652
+  10            78           683           425         418.8     177.87874
No difference proven at 95.0% confidence



System:
x system.chdir
+ system.nochdir
+-------------------------------------------------------------------------+
|x  x   xx    xx            x    x  +   +    ++  +     +  + ++           +|
| |______M___A_________|                                                  |
|                                        |__________A__________|          |
+-------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x  10          1270          1782        1398.5        1454.6     167.10755
+  10          1821          2419        2082.5        2088.7     178.40344
Difference at 95.0% confidence
        634.1 +/- 162.407
        43.5927% +/- 11.1651%
        (Student's t, pooled s = 172.848)




So, yep, chdir wins hard in system time.


-- 
Matthew Fuller     (MF4839)   |  fullermd at over-yonder.net
Systems/Network Administrator |  http://www.over-yonder.net/~fullermd/
           On the Internet, nobody can hear you scream.