Kernel SRU request submitted for groovy and focal - and PATCH for hirsute: https://lists.ubuntu.com/archives/kernel-team/2021-March/thread.html#118639 changing status to 'In Progress' for all entries (F, G and H).
** Description changed: + 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. + 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.. ** Changed in: linux (Ubuntu Focal) Assignee: (unassigned) => Canonical Kernel Team (canonical-kernel-team) ** Changed in: linux (Ubuntu Groovy) Assignee: (unassigned) => Canonical Kernel Team (canonical-kernel-team) ** Changed in: linux (Ubuntu Hirsute) Assignee: Frank Heimes (fheimes) => Canonical Kernel Team (canonical-kernel-team) ** Changed in: linux (Ubuntu Focal) Importance: Undecided => High ** Changed in: linux (Ubuntu Groovy) Importance: Undecided => High ** Changed in: linux (Ubuntu Hirsute) Importance: Undecided => High ** Changed in: linux (Ubuntu Hirsute) Status: New => In Progress ** Changed in: linux (Ubuntu Groovy) Status: New => In Progress ** Changed in: linux (Ubuntu Focal) Status: New => In Progress -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1921498 Title: [UBUNUT 21.04] s390/vtime: fix increased steal time accounting To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-z-systems/+bug/1921498/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs