From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: Network shutdown under load Date: Wed, 10 Feb 2010 13:31:34 -0600 Message-ID: <4B730996.5000608@codemonkey.ws> References: <201001291406.41559.tahm@linux.vnet.ibm.com> <201002081010.03751.tahm@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, qemu-devel@nongnu.org, chrisw@redhat.com, avi@redhat.com, herbert@gondor.apana.org.au, rek2@binaryfreedom.info, markmc@redhat.com, aliguori@us.ibm.com To: Tom Lendacky Return-path: Received: from mail-gx0-f224.google.com ([209.85.217.224]:53639 "EHLO mail-gx0-f224.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754180Ab0BJTbj (ORCPT ); Wed, 10 Feb 2010 14:31:39 -0500 Received: by gxk24 with SMTP id 24so372242gxk.1 for ; Wed, 10 Feb 2010 11:31:38 -0800 (PST) In-Reply-To: <201002081010.03751.tahm@linux.vnet.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: On 02/08/2010 10:10 AM, Tom Lendacky wrote: > Fix a race condition where qemu finds that there are not enough virtio > ring buffers available and the guest make more buffers available before > qemu can enable notifications. > > Signed-off-by: Tom Lendacky > Signed-off-by: Anthony Liguori > Applied. Thanks. We should audit the code for proper barrier support. Right now, I think there's a lot of places that we're missing them. Regards, Anthony Liguori > hw/virtio-net.c | 10 +++++++++- > 1 files changed, 9 insertions(+), 1 deletions(-) > > diff --git a/hw/virtio-net.c b/hw/virtio-net.c > index 6e48997..5c0093e 100644 > --- a/hw/virtio-net.c > +++ b/hw/virtio-net.c > @@ -379,7 +379,15 @@ static int virtio_net_has_buffers(VirtIONet *n, int bufsize) > (n->mergeable_rx_bufs&& > !virtqueue_avail_bytes(n->rx_vq, bufsize, 0))) { > virtio_queue_set_notification(n->rx_vq, 1); > - return 0; > + > + /* To avoid a race condition where the guest has made some buffers > + * available after the above check but before notification was > + * enabled, check for available buffers again. > + */ > + if (virtio_queue_empty(n->rx_vq) || > + (n->mergeable_rx_bufs&& > + !virtqueue_avail_bytes(n->rx_vq, bufsize, 0))) > + return 0; > } > > virtio_queue_set_notification(n->rx_vq, 0); > > On Friday 29 January 2010 02:06:41 pm Tom Lendacky wrote: > >> There's been some discussion of this already in the kvm list, but I want to >> summarize what I've found and also include the qemu-devel list in an effort >> to find a solution to this problem. >> >> Running a netperf test between two kvm guests results in the guest's >> network interface shutting down. I originally found this using kvm guests >> on two different machines that were connected via a 10GbE link. However, >> I found this problem can be easily reproduced using two guests on the same >> machine. >> >> I am running the 2.6.32 level of the kvm.git tree and the 0.12.1.2 level of >> the qemu-kvm.git tree. >> >> The setup includes two bridges, br0 and br1. >> >> The commands used to start the guests are as follows: >> usr/local/bin/qemu-system-x86_64 -name cape-vm001 -m 1024 -drive >> file=/autobench/var/tmp/cape-vm001- >> raw.img,if=virtio,index=0,media=disk,boot=on -net >> nic,model=virtio,vlan=0,macaddr=00:16:3E:00:62:51,netdev=cape-vm001-eth0 - >> netdev tap,id=cape-vm001-eth0,script=/autobench/var/tmp/ifup-kvm- >> br0,downscript=/autobench/var/tmp/ifdown-kvm-br0 -net >> nic,model=virtio,vlan=1,macaddr=00:16:3E:00:62:D1,netdev=cape-vm001-eth1 - >> netdev tap,id=cape-vm001-eth1,script=/autobench/var/tmp/ifup-kvm- >> br1,downscript=/autobench/var/tmp/ifdown-kvm-br1 -vnc :1 -monitor >> telnet::5701,server,nowait -snapshot -daemonize >> >> usr/local/bin/qemu-system-x86_64 -name cape-vm002 -m 1024 -drive >> file=/autobench/var/tmp/cape-vm002- >> raw.img,if=virtio,index=0,media=disk,boot=on -net >> nic,model=virtio,vlan=0,macaddr=00:16:3E:00:62:61,netdev=cape-vm002-eth0 - >> netdev tap,id=cape-vm002-eth0,script=/autobench/var/tmp/ifup-kvm- >> br0,downscript=/autobench/var/tmp/ifdown-kvm-br0 -net >> nic,model=virtio,vlan=1,macaddr=00:16:3E:00:62:E1,netdev=cape-vm002-eth1 - >> netdev tap,id=cape-vm002-eth1,script=/autobench/var/tmp/ifup-kvm- >> br1,downscript=/autobench/var/tmp/ifdown-kvm-br1 -vnc :2 -monitor >> telnet::5702,server,nowait -snapshot -daemonize >> >> The ifup-kvm-br0 script takes the (first) qemu created tap device and >> brings it up and adds it to bridge br0. The ifup-kvm-br1 script take the >> (second) qemu created tap device and brings it up and adds it to bridge >> br1. >> >> Each ethernet device within a guest is on it's own subnet. For example: >> guest 1 eth0 has addr 192.168.100.32 and eth1 has addr 192.168.101.32 >> guest 2 eth0 has addr 192.168.100.64 and eth1 has addr 192.168.101.64 >> >> On one of the guests run netserver: >> netserver -L 192.168.101.32 -p 12000 >> >> On the other guest run netperf: >> netperf -L 192.168.101.64 -H 192.168.101.32 -p 12000 -t TCP_STREAM -l 60 >> -c -C -- -m 16K -M 16K >> >> It may take more than one netperf run (I find that my second run almost >> always causes the shutdown) but the network on the eth1 links will stop >> working. >> >> I did some debugging and found that in qemu on the guest running netserver: >> - the receive_disabled variable is set and never gets reset >> - the read_poll event handler for the eth1 tap device is disabled and >> never re-enabled >> These conditions result in no packets being read from the tap device and >> sent to the guest - effectively shutting down the network. Network >> connectivity can be restored by shutting down the guest interfaces, >> unloading the virtio_net module, re-loading the virtio_net module and >> re-starting the guest interfaces. >> >> I'm continuing to work on debugging this, but would appreciate if some >> folks with more qemu network experience could try to recreate and debug >> this. >> >> If my kernel config matters, I can provide that. >> >> Thanks, >> Tom >> -- >> To unsubscribe from this list: send the line "unsubscribe kvm" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >> > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > >