[UBUNTU 20.04] PSI generates overhead on s390x
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
Ubuntu on IBM z Systems |
Fix Released
|
Medium
|
Skipper Bug Screeners | ||
linux (Ubuntu) |
Fix Released
|
Undecided
|
Canonical Kernel Team | ||
Focal |
Fix Released
|
Undecided
|
Unassigned |
Bug Description
SRU Justification:
==================
[Impact]
* PSI is enabled by default for all architectures in Ubuntu.
* On s390x this leads to performance degradations on popular workloads like web serving (nginx).
[Fix]
* Leave 'CONFIG_PSI=y', but change 'CONFIG_
[Test Case]
* Measure the overhead with 'CONFIG_
[Regression Potential]
* The regression potential can be considered as moderate, since PSI (Pressure stall information tracking),
* since PSI is just used to collect CPU overcommitted, memory and IO metrics.
* And it can be enabled again with the kernel argument.
__________
PSI is always enabled in Ubuntu 20.04.
For a test system with 72 guests on 8 cores running a nginx workload this created an overhead of ~1%.
Can we change this back to
CONFIG_PSI=y
CONFIG_
so that by default the overhead is not there but for debugging or if needed it can still be enabled via kernel parm?
Maybe there has been a reason for this - so feel free to discuss.
---uname output---
Linux t35lp76 5.4.0-26-generic #30-Ubuntu SMP Mon Apr 20 16:57:22 UTC 2020 s390x s390x s390x GNU/Linux
Machine Type = All s390x architecture
---Debugger---
A debugger is not configured
---Steps to Reproduce---
root@t35lp76:
CONFIG_PSI=y
# CONFIG_
Stack trace output:
no
Oops output:
no
System Dump Info:
The system is not configured to capture a system dump.
*Additional Instructions for epasch@de,ibm.com:
-Attach sysctl -a output output to the bug.
CVE References
tags: | added: architecture-s3903164 bugnameltc-185697 severity-medium targetmilestone-inin--- |
Changed in ubuntu: | |
assignee: | nobody → Skipper Bug Screeners (skipper-screen-team) |
affects: | ubuntu → linux (Ubuntu) |
Changed in linux (Ubuntu): | |
assignee: | Skipper Bug Screeners (skipper-screen-team) → Canonical Kernel Team (canonical-kernel-team) |
Changed in ubuntu-z-systems: | |
assignee: | nobody → Skipper Bug Screeners (skipper-screen-team) |
importance: | Undecided → Medium |
status: | New → Triaged |
summary: |
- [UBUNTU 20.04] Overhead introduced by PSI + [UBUNTU 20.04] PSI generated overhead on s390x |
summary: |
- [UBUNTU 20.04] PSI generated overhead on s390x + [UBUNTU 20.04] PSI generates overhead on s390x |
Changed in linux (Ubuntu Focal): | |
status: | New → In Progress |
Changed in linux (Ubuntu Focal): | |
status: | In Progress → Fix Committed |
Changed in ubuntu-z-systems: | |
status: | In Progress → Fix Committed |
Changed in ubuntu-z-systems: | |
status: | Fix Committed → Fix Released |
Request submitted to kernel team's mailing list: /lists. ubuntu. com/archives/ kernel- team/2020- May/thread. html#109592
https:/
changing status to 'In Progress'