[Bug 171811] [patch] rctl(8) cputime is too high

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=171811

olevole at olevole.ru changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |olevole at olevole.ru

--- Comment #3 from olevole at olevole.ru ---
Since this problem can not be fixed for a long time it may be the best solution
to add one more line into 'BUGS' of rctl(8) https://man.freebsd.org/rctl/8

At the moment (end of 2017) this problem has not been fixed in any supported
FreeBSD version and this problem makes it impossible to have the correct
statistics on the jail and makes it dangerous for people who use a billing
system based on RACCT.

This problem also affects 'pcpu' metrics ( %CPU, in percents of a single CPU
core ) and can be easy to reproduce on single core:

1) Run jail1
2) Try to execute ant fast/light external command (e.g. /bin/ls ) in the loop.
Or compile this sample as /root/a.out in jail:

---
#include <stdio.h>

int main()
{
return 0
}
---

Write execution loop and drop it into jail, e.g /root/run.sh:
---
#!/bin/sh

while [ 1 ]; do
/root/a.out > /dev/null
done
---

Run inside jail this script via:

cpuset -c -l 0 /bin/sh /root/run.sh


After this we can see on the 'top -P':
---
182 processes: 2 running, 180 sleeping
CPU 0: 34.1% user,  0.0% nice, 65.9% system,  0.0% interrupt,  0.0% idle
CPU 1:  0.5% user,  0.0% nice,  0.0% system,  0.0% interrupt, 99.5% idle
CPU 2:  3.1% user,  0.0% nice,  1.2% system,  0.0% interrupt, 95.7% idle
CPU 3:  0.0% user,  0.0% nice,  0.4% system,  0.0% interrupt, 99.6% idle
CPU 4:  1.2% user,  0.0% nice,  0.8% system,  0.0% interrupt, 98.1% idle
CPU 5:  0.8% user,  0.0% nice,  0.4% system,  0.0% interrupt, 98.8% idle
CPU 6:  1.2% user,  0.0% nice,  0.0% system,  0.0% interrupt, 98.8% idle
CPU 7:  0.4% user,  0.0% nice,  0.4% system,  0.0% interrupt, 99.2% idle
...

  PID USERNAME       THR PRI NICE   SIZE    RES STATE   C   TIME    WCPU
COMMAND
41437 root             1  76    0 11408K  2232K CPU0    0   0:07  12.79% sh
...
---


Only one core is busy. However if we look at the RACCT from the hoster side, we
see the following picture:

freebsd:~ # rctl -u jail:jail1 | grep pcpu
pcpu=25600
freebsd:~ # rctl -u jail:jail1 | grep pcpu
pcpu=25600
freebsd:~ # rctl -u jail:jail1 | grep pcpu
pcpu=25600


Unfortunately this is not an unlikely reproduction of the problem.
Similar you can see in real life very often, for example at the configuration
stage when a large number of commands are executed:

Try to execute in the jail, for example:

env BATCH=no make -C /usr/ports/misc/mc clean configure

And you will see the problem of statistics again

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