Re: [PATCH] kvm: Drop obsolete cpu_get/put in make_all_cpus_request

[Jan Kiszka <jan.kiszka@siemens.com>]

Marcelo Tosatti wrote:
> Jan,
> 
> This was suggested but we thought it might be safer to keep the
> get_cpu/put_cpu pair in case -rt kernels require it (which might be
> bullshit, but nobody verified).

-rt stumbles over both patterns (that's why I stumbled over it in the
first place: get_cpu disables preemption, but spin_lock is a sleeping
lock under -rt) and actually requires requests_lock to become
raw_spinlock_t. Reordering get_cpu and spin_lock would be another
option, but not really a gain for both scenarios.

So unless there is a way to make the whole critical section preemptible
(thus migration-agnostic), I think we can micro-optimize it like this.

Jan

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