Bug 235556
| Summary: | rctl(8) pcpu/cputime is too high | ||
|---|---|---|---|
| Product: | Base System | Reporter: | Oleg Ginzburg <olevole> |
| Component: | kern | Assignee: | freebsd-bugs (Nobody) <bugs> |
| Status: | New --- | ||
| Severity: | Affects Many People | CC: | allanjude, cyril, markj |
| Priority: | --- | ||
| Version: | CURRENT | ||
| Hardware: | Any | ||
| OS: | Any | ||
|
Description
Oleg Ginzburg
2019-02-06 15:51:17 UTC
Can you freshly describe the problem and provide some reproduction steps? RACCT pcpu metrics are incorrect when processes end quickly.
What i expect:
maximum value for 1-core process: 100
What i get:
100x256
It is not an artificial or abstract state. For example this behavior is easy to see when working 'make config' for autotools with the launch of a lot of short calls (e.g env BATCH=no make -C /usr/ports/misc/mc clean configure). This makes it impossible to use any external billing based on RACCT.
How to reproduce ( we use cpuset here to create load on only one core. So we should have pcpu=100 for jail assuming the jail does nothing else ):
1) Run jail1
2) Try to execute ant fast/light external command (e.g. /bin/ls ) in the loop.
For more convincing create a simple utility:
---
#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:
cpuset -c -l 0 /bin/sh /root/run.sh
After this we can see on the 'top -P' something like:
---
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:
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
I've created a patch here: https://reviews.freebsd.org/D30632 which seems to fix this problem. (In reply to cyril from comment #3) I confirm - everything is fine now. Tested on: FreeBSD 14.0-CURRENT #0 main-n247127-1976e079544-dirty amd64 (In reply to Oleg Ginzburg from comment #4) markj discovered that the above patch is actually not correct. I have made another patch that modifies how pcpu is calculated. It is now based on the elapsed cputime value divided by the elapsed realtime value, rather than aggregating the pcpu of all processes in a jail. You can try the patch here: https://reviews.freebsd.org/D30878 |
