From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH] vhost: force vhost off for non-MSI guests Date: Thu, 20 Jan 2011 19:47:21 +0200 Message-ID: <20110120174721.GA25813@redhat.com> References: <20110120153521.GA24357@redhat.com> <1295541113.24174.4.camel@sridhar.beaverton.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Alex Williamson , Juan Quintela , jasowang@redhat.com, Jes.Sorensen@redhat.com, kvm@vger.kernel.org, qemu-devel@nongnu.org To: Sridhar Samudrala Return-path: Received: from mx1.redhat.com ([209.132.183.28]:64410 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751833Ab1ATRrk (ORCPT ); Thu, 20 Jan 2011 12:47:40 -0500 Content-Disposition: inline In-Reply-To: <1295541113.24174.4.camel@sridhar.beaverton.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: On Thu, Jan 20, 2011 at 08:31:53AM -0800, Sridhar Samudrala wrote: > On Thu, 2011-01-20 at 17:35 +0200, Michael S. Tsirkin wrote: > > When MSI is off, each interrupt needs to be bounced through the io > > thread when it's set/cleared, so vhost-net causes more context switches and > > higher CPU utilization than userspace virtio which handles networking in > > the same thread. > > > > We'll need to fix this by adding level irq support in kvm irqfd, > > for now disable vhost-net in these configurations. > > > > Signed-off-by: Michael S. Tsirkin > > --- > > > > I need to report some error from virtio-pci > > that would be handled specially (disable but don't > > report an error) so I wanted one that's never likely to be used by a > > userspace ioctl. I selected ERANGE but it'd > > be easy to switch to something else. Comments? > > Should this error be EVHOST_DISABLED rather than EVIRTIO_DISABLED? > > -Sridhar The error is reported by virtio-pci which does not know about vhost. I started with EVIRTIO_MSIX_DISABLED and made is shorter. Would EVIRTIO_MSIX_DISABLED be better? > > > > hw/vhost.c | 4 +++- > > hw/virtio-net.c | 6 ++++-- > > hw/virtio-pci.c | 3 +++ > > hw/virtio.h | 2 ++ > > 4 files changed, 12 insertions(+), 3 deletions(-) > > > > diff --git a/hw/vhost.c b/hw/vhost.c > > index 1d09ed0..c79765a 100644 > > --- a/hw/vhost.c > > +++ b/hw/vhost.c > > @@ -649,7 +649,9 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev) > > > > r = vdev->binding->set_guest_notifiers(vdev->binding_opaque, true); > > if (r < 0) { > > - fprintf(stderr, "Error binding guest notifier: %d\n", -r); > > + if (r != -EVIRTIO_DISABLED) { > > + fprintf(stderr, "Error binding guest notifier: %d\n", -r); > > + } > > goto fail_notifiers; > > } > > > > diff --git a/hw/virtio-net.c b/hw/virtio-net.c > > index ccb3e63..5de3fee 100644 > > --- a/hw/virtio-net.c > > +++ b/hw/virtio-net.c > > @@ -121,8 +121,10 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t status) > > if (!n->vhost_started) { > > int r = vhost_net_start(tap_get_vhost_net(n->nic->nc.peer), &n->vdev); > > if (r < 0) { > > - error_report("unable to start vhost net: %d: " > > - "falling back on userspace virtio", -r); > > + if (r != -EVIRTIO_DISABLED) { > > + error_report("unable to start vhost net: %d: " > > + "falling back on userspace virtio", -r); > > + } > > } else { > > n->vhost_started = 1; > > } > > diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c > > index dd8887a..dbf4be0 100644 > > --- a/hw/virtio-pci.c > > +++ b/hw/virtio-pci.c > > @@ -628,6 +628,9 @@ static int virtio_pci_set_guest_notifier(void *opaque, int n, bool assign) > > EventNotifier *notifier = virtio_queue_get_guest_notifier(vq); > > > > if (assign) { > > + if (!msix_enabled(&proxy->pci_dev)) { > > + return -EVIRTIO_DISABLED; > > + } > > int r = event_notifier_init(notifier, 0); > > if (r < 0) { > > return r; > > diff --git a/hw/virtio.h b/hw/virtio.h > > index d8546d5..53bbdba 100644 > > --- a/hw/virtio.h > > +++ b/hw/virtio.h > > @@ -98,6 +98,8 @@ typedef struct { > > void (*vmstate_change)(void * opaque, bool running); > > } VirtIOBindings; > > > > +#define EVIRTIO_DISABLED ERANGE > > + > > #define VIRTIO_PCI_QUEUE_MAX 64 > > > > #define VIRTIO_NO_VECTOR 0xffff