New pid namespaces patches testing

[Eric W. Biederman]

Pavel Emelianov <xemul at openvz.org> writes:

> OK. We have measured the nptl perf test for init namespace.
> Summary - flat model is very light, Suka's patches break the 
> kernel performance event when CONFIG_PID_NS is off.
>
>                  |    perf, s   | perf loss  |
> -----------------+--------------+------------+
> 2.6.22-rc4-mm2   | 13.79 ± 0.13 |    ---     |
>                  |              |            |
> suka  + PID_NS=n | 14.07 ± 0.13 |    2.0%    |
> suka  + PID_NS=y | 14.06 ± 0.08 |    2.0%    |
>                  |              |            |
> pavel + PID_NS=n | 13.80 ± 0.07 |    0.0%    |
> pavel + FLAT     | 13.80 ± 0.07 |    0.0%    |
> pavel + MULTI    | 14.28 ± 0.08 |    3.5%    |
> -----------------+--------------+------------+
>
> I do believe that Suka's hierarchical model is better than mine,
> but my point is: let's support the flat model as well.

If performance is to be the deciding factor between implementations,
then we need to do the research and see what specifically makes the
difference in performance.

My hunch is the real difference in Sukas patches is the extra memory
allocation, or some other stupid silly thing that we can optimize out
and make things simpler, faster, and more maintainable.

Eric