[SRU][F][PATCH 0/1] Ubuntu: [Config] PSI generates overhead on s390x

[frank.heimes at canonical.com]

Buglink: https://bugs.launchpad.net/bugs/1876044

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_PSI_DEFAULT_DISABLED=n' to 'CONFIG_PSI_DEFAULT_DISABLED=y'

[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 metrics.

* And it can be enabled again with the kernel argument.

Frank Heimes (1):
  CONFIG_PSI is enabled by default, but creates additional overhead on
    s390x, hence should be disabled by default on s390x only.

 debian.master/config/annotations          | 4 +++-
 debian.master/config/config.common.ubuntu | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

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2.25.1