Re: [PATCH] sched: Decouple PREFERRED_CPU from PARAVIRT

[sashiko-bot@kernel.org]

> PREFERRED_CPU mechanism does not rely on any feature introduced by PARAVIRT
> but PREFERRED_CPU still gated behind PARAVIRT. Any architecture that
> would like to enable PREFERRED_CPU mechanism has to also enable PARAVIRT
> and bring additional changes to accommodate PARAVIRT's requirements.
> 
> As an example, s390 doesn't enable PARAVIRT config for hardware virtualized
> Logical Partitions (LPAR). The steal time is accounted for the LPARs via
> architecture's own steal time accounting mechanism instead of the common
> steal time infrastructure PARAVIRT supplies.
> For s390 to enable PREFERRED_CPU, PRAVIRT and its required stubs are
> just unncessary.
> 
> Based on the discussion between Yury Norov and Peter Zijlstra over
> Yury's original patch [1]:
> 
> Introduce a new config flag HAVE_CPUTIME_STEAL to indicate that the
> architecture has steal time measurement capabilities already implemented
> and to signal that PARAVIRT is not required.
> Remove PARAVIRT gating from CPU_PREFERRED and add HAVE_CPUTIME_STEAL
> instead.
> Select HAVE_CPUTIME_STEAL for s390 and powerpc-pseries configs.
> 
> [1] https://lore.kernel.org/all/20261101192203.6979-2-ynorov@nvidia.com/
> 
> Reviewed-by: Yury Norov <ynorov@nvidia.com>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Mete Durlu <meted@linux.ibm.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261106-preferredcpu-v1-1-3f0ca4944f8b@linux.ibm.com?part=1