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

[Paolo Bonzini]

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