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
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https://bugs.launchpad.net/bugs/1921498
Title:
[UBUNUT 21.04] s390/vtime: fix increased steal time accounting
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