The commit "s390/vtime: fix increased steal time accounting" landed in hirsute
as c64e48d4ace3 in kernel Ubuntu-5.11.0-14 and this kernel is in hirsute's
release pocket:
linux-generic | 5.11.0.14.15 | hirsute | s390x
Hence closing the hirsute entry as Fix Released.
** Changed in: linux (Ubuntu Hirsute)
Status: In Progress => Fix Released
--
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/1921498
Title:
[UBUNUT 21.04] s390/vtime: fix increased steal time accounting
Status in Ubuntu on IBM z Systems:
Fix Committed
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Focal:
Fix Committed
Status in linux source package in Groovy:
Fix Committed
Status in linux source package in Hirsute:
Fix Released
Bug description:
SRU Justification:
==================
[Impact]
* The reported steal time on s390x is erroneously increasing and
therefore broken.
* This problem got introduced with commit 152e9b8676c6e
("s390/vtime: steal time exponential moving average") - upstream with v5.1
[Fix]
* d54cb7d54877d529bc1e0e1f47a3dd082f73add3 d54cb7d54877 "s390/vtime:
fix increased steal time accounting"
[Test Case]
* An IBM Z or LinuxONE systems, installed with Ubuntu Server 20.04,
20.10 and 21.04 on LPAR, are needed.
* The system needs to be configured as KVM host with one or more KVM
guests.
* Now put significant workload on the guest(s), so that the hypervisor starts
to 'steal time'.
This can be best forced by having only very limited CPU resources for the
hypervisor itself.
* Start monitoring the steal time, that is reported at /proc/stat,
but can be more easily verified with tools like vmstat or even top.
* If the steal time starts ever growing (exponentially), the situation
is broken.
* In case the steal time stays relatively constant,
or grows only very limited after a ramp up phase of some minutes,
or just oscillates around a certain value, a fixed/patched kernel is in use.
[Regression Potential]
* The patch only changes the single line that calculates:
account_steal_time
* In case the account_steal_time calculation is still broken after the
modification,
the steal time is just again not reported correctly on s390x,
but maybe in a different way (rather than exponentially growing).
* But it will not further harm virtualization on s390x systems.
* The modification is very limited with that one line change.
* The commit got upstream accepted with 5.12-rc4.
[Other]
* Since the patch is needed for kernel higher than 5.1 and got upstream
accepted with 5.12-rc4,
hirsute, groovy and focal are affected.
* The upstream commit can be cleanly cherry-picked from all three affected
Ubuntu releases.
__________
Description: s390/vtime: fix increased steal time accounting
Symptom: Increased steal time values.
Problem: Commit 152e9b8676c6e ("s390/vtime: steal time exponential
moving average") inadvertently changed the input value for
account_steal_time() from "cputime_to_nsecs(steal)" to just
"steal", resulting in broken increased steal time accounting.
Solution: Fix this by changing it back to "cputime_to_nsecs(steal)".
Reproduction: -
Upstream-ID: d54cb7d54877d529bc1e0e1f47a3dd082f73add3
Stable tagged : kernel 5.1.
Therefore only to be applyable for focal, groovy, hirsuite.
Due to stable tag integration , only for integration checking..
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu-z-systems/+bug/1921498/+subscriptions
--
Mailing list: https://launchpad.net/~kernel-packages
Post to : kernel-packages@lists.launchpad.net
Unsubscribe : https://launchpad.net/~kernel-packages
More help : https://help.launchpad.net/ListHelp
