From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v2 1/2] KVM: MMIO: Lock coalesced device when checking for available entry Date: Mon, 18 Jul 2011 11:11:57 +0300 Message-ID: <4E23EACD.1020407@redhat.com> References: <1310729869-1451-1-git-send-email-levinsasha928@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, Ingo Molnar , Marcelo Tosatti , Pekka Enberg To: Sasha Levin Return-path: Received: from mx1.redhat.com ([209.132.183.28]:5527 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751973Ab1GRIMN (ORCPT ); Mon, 18 Jul 2011 04:12:13 -0400 In-Reply-To: <1310729869-1451-1-git-send-email-levinsasha928@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: On 07/15/2011 02:37 PM, Sasha Levin wrote: > Move the check whether there are available entries to within the spinlock. > This allows working with larger amount of VCPUs and reduces premature > exits when using a large number of VCPUs. > > Cc: Avi Kivity > Cc: Ingo Molnar > Cc: Marcelo Tosatti > Cc: Pekka Enberg > Signed-off-by: Sasha Levin > --- > virt/kvm/coalesced_mmio.c | 9 ++++++--- > 1 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c > index fc84875..34188db 100644 > --- a/virt/kvm/coalesced_mmio.c > +++ b/virt/kvm/coalesced_mmio.c > @@ -37,7 +37,7 @@ static int coalesced_mmio_in_range(struct kvm_coalesced_mmio_dev *dev, > */ > ring = dev->kvm->coalesced_mmio_ring; > avail = (ring->first - ring->last - 1) % KVM_COALESCED_MMIO_MAX; > - if (avail< KVM_MAX_VCPUS) { > + if (avail == 0) { > /* full */ > return 0; > } > @@ -63,11 +63,14 @@ static int coalesced_mmio_write(struct kvm_io_device *this, > { > struct kvm_coalesced_mmio_dev *dev = to_mmio(this); > struct kvm_coalesced_mmio_ring *ring = dev->kvm->coalesced_mmio_ring; > - if (!coalesced_mmio_in_range(dev, addr, len)) > - return -EOPNOTSUPP; > > spin_lock(&dev->lock); > > + if (!coalesced_mmio_in_range(dev, addr, len)) { > + spin_unlock(&dev->lock); > + return -EOPNOTSUPP; > + } > + > /* copy data in first free entry of the ring */ Hmm. This means we take the lock for every I/O, whether it hits coalesced mmio or not. We need to do the range check before taking the lock and the space check after taking the lock. -- error compiling committee.c: too many arguments to function