On Thu, Oct 29, 2026 at 02:32:08PM +0100, Mete Durlu wrote: > On 28/09/2026 07:37, Shrikanth Hegde wrote: > > Provide the preferred CPU infrastructure. Define get/set macros > > which could be used to get/set CPU state as preferred. > > > > CONFIG_PREFERRED_CPU will be selected by the driver which handles > > steal time values. It is going to set/clear preferred CPU state. > > This driver will be called steal_governor and it is introduced in > > subsequent patches. It periodically computes the steal ratio and > > decides on preferred CPU state. > > > > A CPU is set to preferred when it becomes active. Later it may be > > marked as non-preferred depending on steal ratio by the steal_governor. > > > > Always maintain design construct of preferred is subset of active. > > i.e. preferred ⊆ active ⊆ online ⊆ present ⊆ possible > > > > With CONFIG_PREFERRED_CPU=n, ensure set_cpu_preferred is a nop and get > > method returns the active state in that case. > > > > Signed-off-by: Shrikanth Hegde <[email protected]> > > --- > > include/linux/cpumask.h | 24 ++++++++++++++++++++++++ > > kernel/Kconfig.preempt | 4 ++++ > > kernel/cpu.c | 6 ++++++ > > kernel/sched/core.c | 5 +++++ > > 4 files changed, 39 insertions(+) > > [..snip..] > > > #define cpu_is_offline(cpu) unlikely(!cpu_online(cpu)) > > diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt > > index 985aea617cfe..edc067a0c422 100644 > > --- a/kernel/Kconfig.preempt > > +++ b/kernel/Kconfig.preempt > > @@ -194,3 +194,7 @@ config SCHED_CLASS_EXT > > For more information: > > Documentation/scheduler/sched-ext.rst > > https://github.com/sched-ext/scx > > + > > +config PREFERRED_CPU > > + bool > > + depends on SMP && PARAVIRT > FWICT, PREFERRED_CPU mechanism can work perfectly fine without PARAVIRT > selected. It would be annoying to enable it and implement a dummy > paravirt_steal_clock() just for that. > > Shrikanth, would it be possible to drop that dependency?
Do you have a non-paravirt case in mind? I'm actually about to submit an RFC that drops the PARAVIRT dependency and provides write access to the preferred mask. But I want to make sure that we need it, and we've got no reasonable mechanism to put unneeded CPUs on idle already. Simply relaxing the PARAVIRT dependency without a solid use case would bloat configuration space for nothing. If you've got such a case in mind, the rest is trivial. Thanks, Yury
