From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: Unable to create more than 1 guest virtio-net device using vhost-net backend Date: Sun, 21 Mar 2010 12:21:43 +0200 Message-ID: <20100321102143.GC13522@redhat.com> References: <1269037167.5127.12.camel@w-sridhar.beaverton.ibm.com> <20100321095544.GA6443@redhat.com> <4BA5F0D5.6020801@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Michael S. Tsirkin" , Sridhar Samudrala , netdev , "kvm@vger.kernel.org" To: Avi Kivity Return-path: Content-Disposition: inline In-Reply-To: <4BA5F0D5.6020801@redhat.com> Sender: kvm-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Sun, Mar 21, 2010 at 12:11:33PM +0200, Avi Kivity wrote: > On 03/21/2010 11:55 AM, Michael S. Tsirkin wrote: > >On Fri, Mar 19, 2010 at 03:19:27PM -0700, Sridhar Samudrala wrote: > >>When creating a guest with 2 virtio-net interfaces, i am running > >>into a issue causing the 2nd i/f falling back to userpace virtio > >>even when vhost is enabled. > >> > >>After some debugging, it turned out that KVM_IOEVENTFD ioctl() > >>call in qemu is failing with ENOSPC. > >>This is because of the NR_IOBUS_DEVS(6) limit in kvm_io_bus_register_dev() > >>routine in the host kernel. > >> > >>I think we need to increase this limit if we want to support multiple > >>network interfaces using vhost-net. > >>Is there an alternate solution? > >> > >>Thanks > >>Sridhar > >Nothing easy that I can see. Each device needs 2 of these. Avi, Gleb, > >any objections to increasing the limit to say 16? That would give us > >5 more devices to the limit of 6 per guest. > > Increase it to 200, then. > Currently on each device read/write we iterate over all registered devices. This is not scalable. > Is the limit visible to userspace? If not, we need to expose it. > > -- > error compiling committee.c: too many arguments to function -- Gleb.