On 2/23/21 12:05 PM, Catalin Marinas wrote:

quoted

I totally agree on this point. In the case of runtime switching we might need
the rethink completely the strategy and depends a lot on what we want to allow
and what not. For the kernel I imagine we will need to expose something in sysfs
that affects all the cores and then maybe stop_machine() to propagate it to all
the cores. Do you think having some of the cores running in sync mode and some
in async is a viable solution?

stop_machine() is an option indeed. I think it's still possible to run
some cores in async while others in sync but the static key here would
only be toggled when no async CPUs are left.

In such a case we might need to track the state based on cpuid() and have a mask
that tells us when cpus are all sync.
Not as expensive as stop_machine() but still requires a valid use case to be
introduced according to me.

-- 
Regards,
Vincenzo

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