From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tom Lendacky Subject: Re: Network shutdown under load Date: Mon, 8 Feb 2010 10:10:01 -0600 Message-ID: <201002081010.03751.tahm@linux.vnet.ibm.com> References: <201001291406.41559.tahm@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Cc: 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: kvm@vger.kernel.org Return-path: Received: from e31.co.us.ibm.com ([32.97.110.149]:55753 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752983Ab0BHQKW (ORCPT ); Mon, 8 Feb 2010 11:10:22 -0500 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e31.co.us.ibm.com (8.14.3/8.13.1) with ESMTP id o18G1rtb012129 for ; Mon, 8 Feb 2010 09:01:53 -0700 Received: from d03av05.boulder.ibm.com (d03av05.boulder.ibm.com [9.17.195.85]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id o18GAB7u241400 for ; Mon, 8 Feb 2010 09:10:13 -0700 Received: from d03av05.boulder.ibm.com (loopback [127.0.0.1]) by d03av05.boulder.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id o18GA4Bm014827 for ; Mon, 8 Feb 2010 09:10:06 -0700 In-Reply-To: <201001291406.41559.tahm@linux.vnet.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: 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 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 >