APPLIED: [SRU][R][PATCH 0/2] Remove GENERIC_LOCKBREAK Kconfig option in s390x

[Mehmet Basaran]

Applied to resolute:linux master-next branch. Thanks.

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Massimiliano Pellizzer via kernel-team <kernel-team at lists.ubuntu.com>
writes:

> BugLink: https://bugs.launchpad.net/bugs/2154748
>
> [ Impact ]
>
> s390 selects GENERIC_LOCKBREAK if PREEMPT is enabled. Reason is a historic
> 18 years old commit [1] which fixed a compile error for PREEMPT enabled
> kernels. Back than only PREEMPT_NONE and PREEMPT_VOLUNTARY kernels were
> considered to be important for s390. PREEMPT should "just work".
>
> However, since recently PREEMPT is always enabled [2], which also causes
> GENERIC_LOCKBREAK to be always enabled. For some workloads this leads to
> massive performance degradation; e.g. a simple kernel compile on machines
> with many CPUs may take up to four times longer.
>
> To fix this just remove the GENERIC_LOCKBREAK from s390's Kconfig, since
> the compile error from 18 years ago does not exist anymore.
>
> [1] commit b6b40c532a36 ("[S390] Define GENERIC_LOCKBREAK.")
> [2] commit 7dadeaa6e851 ("sched: Further restrict the preemption modes")
>
> [ Fix ]
>
> Backport commit:
> 1f57f68c4dd1 ("s390: Remove GENERIC_LOCKBREAK Kconfig option")
>
> [ Test Plan ]
>
> Compile and boot tested.
> Tested performance by compiling a kernel and monitoring execution
> with perf.
>
> [ Regression Potential ]
>
> The regression potential of the patch is low.
> It affects only s390x spinlock implementation.
>
> Heiko Carstens (1):
>   s390: Remove GENERIC_LOCKBREAK Kconfig option
>
> Massimiliano Pellizzer (1):
>   UBUNTU [Config]: Remove GENERIC_LOCKBREAK in s390x
>
>  arch/s390/Kconfig                |  3 ---
>  debian.master/config/annotations | 14 +++++++++++++-
>  2 files changed, 13 insertions(+), 4 deletions(-)
>
> --
> 2.53.0
>
>
> --
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team
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