From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754747AbZHPJcj (ORCPT ); Sun, 16 Aug 2009 05:32:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754676AbZHPJcc (ORCPT ); Sun, 16 Aug 2009 05:32:32 -0400 Received: from mx2.redhat.com ([66.187.237.31]:45361 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754060AbZHPJaN (ORCPT ); Sun, 16 Aug 2009 05:30:13 -0400 From: Avi Kivity To: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org Subject: [PATCH 30/48] KVM: Calculate available entries in coalesced mmio ring Date: Sun, 16 Aug 2009 12:29:50 +0300 Message-Id: <1250415008-17175-31-git-send-email-avi@redhat.com> In-Reply-To: <1250415008-17175-1-git-send-email-avi@redhat.com> References: <1250415008-17175-1-git-send-email-avi@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Instead of checking whether we'll wrap around, calculate how many entries are available, and check whether we have enough (just one) for the pending mmio. By itself, this doesn't change anything, but it paves the way for making this function lockless. Signed-off-by: Avi Kivity --- virt/kvm/coalesced_mmio.c | 10 +++++----- 1 files changed, 5 insertions(+), 5 deletions(-) diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c index c4c7ec2..7549068 100644 --- a/virt/kvm/coalesced_mmio.c +++ b/virt/kvm/coalesced_mmio.c @@ -24,7 +24,8 @@ static int coalesced_mmio_in_range(struct kvm_io_device *this, { struct kvm_coalesced_mmio_dev *dev = to_mmio(this); struct kvm_coalesced_mmio_zone *zone; - int next; + struct kvm_coalesced_mmio_ring *ring; + unsigned avail; int i; if (!is_write) @@ -40,10 +41,9 @@ static int coalesced_mmio_in_range(struct kvm_io_device *this, * check if we don't meet the first used entry * there is always one unused entry in the buffer */ - - next = (dev->kvm->coalesced_mmio_ring->last + 1) % - KVM_COALESCED_MMIO_MAX; - if (next == dev->kvm->coalesced_mmio_ring->first) { + ring = dev->kvm->coalesced_mmio_ring; + avail = (ring->first - ring->last - 1) % KVM_COALESCED_MMIO_MAX; + if (avail < 1) { /* full */ return 0; } -- 1.6.3.3