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Subject[RFC][PATCH 0/5] uts namespaces: Introduction
Date
Introduce utsname namespaces.  Instead of a single system_utsname
containing hostname domainname etc, a process can request it's
copy of the uts info to be cloned. The data will be copied from
it's original, but any further changes will not be seen by processes
which are not it's children, and vice versa.

This is useful, for instance, for vserver/openvz, which can now clone
a new uts namespace for each new virtual server.

This patchset is based on Kirill Korotaev's Mar 24 submission, taking
comments (in particular from James Morris and Eric Biederman) into
account.

Some performance results are attached. I was mainly curious whether
it would be worth putting the task_struct->uts_ns pointer inside
a #ifdef CONFIG_UTS_NS. The result show that leaving it in when
CONFIG_UTS_NS=n has negligable performance impact, so that is the
approach this patch takes.

-serge

Performance testing was done on a 2-cpu hyperthreaded
x86 box with 16G ram. The following tests were run:
dbench (20 times, four clients, on reiser fs non-isolated partition)
tbench (20 times, 5 connections)
kernbench (20 times)
reaim (20 times ranging from 1 to 15 users)

They were run on 2.6.17-rc1:
pristine
patched, but with !CONFIG_UTS_NS ("disabled")
patched with CONFIG_UTS_NS=y ("enabled")

All results are presented as means +/- 95% confidence interval.

Dbench results:
pristine: 387.080727 +/- 9.344585
patched disabled: 389.524364 +/- 9.574921
patched enabled: 370.155600 +/- 30.127808

Tbench results:
pristine: 388.940100 +/- 18.095104
patched disabled: 389.173700 +/- 23.658035
patched enabled: 394.333200 +/- 25.813393

Kernbench results:
pristine: 70.317500 +/- 0.210833
patched, disabled: 70.860000 +/- 0.179292
patched, enabled: 70.346500 +/- 0.184784

Reaim results:
pristine:
Nclients Mean 95% CI
1 106080.000000 11327.896029
3 236057.142000 18205.544810
5 247867.136000 23536.800062
7 265370.000000 21284.335743
9 262969.936000 18225.497529
11 278256.000000 6230.342816
13 284288.016000 8924.589388
15 286987.170000 7881.034658

patched, disabled:
Nclients Mean 95% CI
1 105400.000000 8739.978241
3 229500.000000 0.000000
5 252325.176667 16685.663423
7 265125.000000 6747.777319
9 271258.645000 11715.635212
11 280662.608333 7775.229351
13 277719.706667 8173.390359
15 278515.421667 10963.211450

patched, enabled:
Nclients Mean 95% CI
1 102000.000000 0.000000
3 224400.000000 14159.870036
5 242963.288000 40529.490781
7 255150.000000 8745.802081
9 270154.284000 8918.863136
11 283134.260000 12239.361252
13 288497.540000 11336.550964
15 280022.728000 8804.882369

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