[Bug 218259] High latency in KVM guests

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https://bugzilla.kernel.org/show_bug.cgi?id=218259

--- Comment #8 from Sean Christopherson (seanjc@xxxxxxxxxx) ---
On Mon, Dec 18, 2023, bugzilla-daemon@xxxxxxxxxx wrote:
> > I think the kernel is preemptible:
> 
> Ya, not fully preemptible (voluntary only), but the important part is that
> KVM
> will drop mmu_lock if there is contention (which is a "requirement" for the
> bug
> that Yan encountered).

For posterity, the above is wrong.  Volutary preemption isn't _supposed_ to
enable
yielding of contended spinlocks/rwlocks, but due to a bug with dynamic
preemption,
the behavior got enabled for all preempt models:

https://lore.kernel.org/all/20240110214723.695930-1-seanjc@xxxxxxxxxx

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