All autopkgtests for the newly accepted linux-oracle-5.4 
(5.4.0-1019.19~18.04.1) for bionic have finished running.
The following regressions have been reported in tests triggered by the package:

zfs-linux/unknown (armhf)

Please visit the excuses page listed below and investigate the failures, 
proceeding afterwards as per the StableReleaseUpdates policy regarding 
autopkgtest regressions [1].


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  [UBUNTU 20.04] PSI generates overhead on s390x

Status in Ubuntu on IBM z Systems:
  Fix Committed
Status in linux package in Ubuntu:
  In Progress
Status in linux source package in Focal:
  Fix Released

Bug description:
  SRU Justification:


  * PSI is enabled by default for all architectures in Ubuntu.

  * On s390x this leads to performance degradations on popular workloads
  like web serving (nginx).


  * Leave 'CONFIG_PSI=y', but change 'CONFIG_PSI_DEFAULT_DISABLED=n' to

  [Test Case]

  * Measure the overhead with 'CONFIG_PSI_DEFAULT_DISABLED=n' and
  'CONFIG_PSI_DEFAULT_DISABLED=y' on the same environment with nginx.

  [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

  * 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

  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

  A debugger is not configured

  ---Steps to Reproduce---
   root@t35lp76:/boot# grep PSI config-5.4.0-26-generic

  Stack trace output:

  Oops output:

  System Dump Info:
    The system is not configured to capture a system dump.

  *Additional Instructions for epasch@de,
  -Attach sysctl -a output output to the bug.

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