Re: [RFC PATCH 11/11] KVM: PPC: Eliminate global spinlock in kvmppc_h_enter

On Thu, Nov 17, 2011 at 10:55:49AM +1100, Paul Mackerras wrote:

quoted

From dfd5bcfac841f8a36593edf60d9fb15e0d633287 Mon Sep 17 00:00:00 2001

From: Paul Mackerras <redacted>
Date: Mon, 14 Nov 2011 13:30:38 +1100
Subject: 

Currently, kvmppc_h_enter takes a spinlock that is global to the guest,
kvm->mmu_lock, in order to check for pending PTE invalidations safely.
On some workloads, kvmppc_h_enter is called heavily and the use of a
global spinlock could compromise scalability.  We already use a per-
guest page spinlock in the form of the bit spinlock on the rmap chain,
and this gives us synchronization with the PTE invalidation side, which
also takes the bit spinlock on the rmap chain for each page being
invalidated.  Thus it is sufficient to check for pending invalidations
while the rmap chain bit spinlock is held.  However, now we require
barriers in mmu_notifier_retry() and in the places where
mmu_notifier_count and mmu_notifier_seq are updated, since we can now
call mmu_notifier_retry() concurrently with updates to those fields.

Signed-off-by: Paul Mackerras <redacted>
---
Cc'd to kvm@vger.kernel.org for review of the generic kvm changes.

Looks good to me.