Re: [PATCH 15/24] kvm: mmu: Wrap mmu_lock cond_resched and needbreak

Paolo Bonzini
2021-01-26T14:41:10Z

On 21/01/21 01:19, Sean Christopherson wrote:
> What if we simply make the common mmu_lock a union? The rwlock_t is
> probably a bit bigger, but that's a few bytes for an entire VM. And
> maybe this would entice/inspire other architectures to move to a similar
> MMU model.

Looking more at this, there is a problem in that MMU notifier functions
take the MMU lock.

Yes, qrwlock the size is a bit larger than qspinlock. However, the fast
path of qrwlocks is small, and if the slow paths are tiny compared to
the mmu_lock critical sections that are so big as to require
cond_resched. So I would consider just changing all architectures to an
rwlock.

Paolo