[Qemu-devel] Network shutdown under load

[Qemu-devel] Network shutdown under load

[Tom Lendacky]

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

[Qemu-devel] Re: Network shutdown under load

[RW]

Hi,

we're currently having this problem on two production servers
that 2-4 times a day one interface shuts down. We've four KVMs
running on two hosts (2x2). All VMs have eth0 and eth1 running virtio_net.
All eth0's are connected to bridge br0 and all eth1's are connected to
br1 on the host. Here are the startup options for one VM (the
others are quite similar [of course other mac address, ...]):

/usr/bin/kvm -m 8192 -smp 8 -cpu host -daemonize -k de -vnc 127.0.0.1:1
-monitor telnet:172.18.105.46:4444,server,nowait -localtime -pidfile
/tmp/kvm-dodoma.pid -drive
file=/data/kvm/kvmimages/dodoma.qcow2,if=virtio,cache=none,boot=on
-drive file=/data/kvm/kvmimages/dodoma-vdb.qcow2,if=virtio,cache=none
-net nic,vlan=104,model=virtio,macaddr=00:ff:48:e5:4b:8d -net
tap,vlan=104,ifname=tap.b.dodoma,script=no -net
nic,vlan=96,model=virtio,macaddr=00:ff:48:e5:4b:8f -net
tap,vlan=96,ifname=tap.f.dodoma,script=no

I've tried the very latest Gentoo kernel 2.6.30 on the host and
guest (all VMs and hosts running Gentoo btw.). With kernel
2.6.31 on host and 2.6.30 on guest the problem still exist. I've
tried KVM 0.11.1, 0.12.1.2 and 0.12.2 running with kernel 2.6.30
and 2.6.31 on the host side.

Interestingly all the VMs almost have the same network traffic
(in and out) but the VMs running Apache bind to eth1 have
the biggest problems. They shut down eth1 2-4 times a day.
eth0 is running fine despite that it is doing almost the same
traffic amount but this traffic comes from the database where
as eth1 sends the traffic to the proxy (Varnish). So incoming traffic
seems to work fine here but outgoing traffic is problematic. On the
other hand the VMs running Varnish getting all the traffic through
eth1. Here I've "only" seen one shutdown of eth1 in 48 hours.

Is there anything I can help to debug this problem? Is there
already a fix available? Otherwise I really have to install KVM-88
which runs fine on some other hosts.

Thanks!
Robert


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
>   

[Qemu-devel] Re: Network shutdown under load

[Tom Lendacky]

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 <toml@us.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

 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
> 

[Qemu-devel] Re: Network shutdown under load

[Anthony Liguori]

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<toml@us.ibm.com>
> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
>    

I've walked through the changes in this series and I'm pretty certain 
that this is the only problem.  I'd appreciate if others could review 
though.

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
>>
>>      

[Qemu-devel] Re: Network shutdown under load

[Herbert Xu]

On Mon, Feb 08, 2010 at 10:10:01AM -0600, 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 <toml@us.ibm.com>
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

Good cath!
 
> 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.
> +         */

We should also add a full memory barrier right here to avoid
out-of-order loads.

> +        if (virtio_queue_empty(n->rx_vq) ||
> +            (n->mergeable_rx_bufs &&
> +             !virtqueue_avail_bytes(n->rx_vq, bufsize, 0)))
> +            return 0;
>      }

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

[Qemu-devel] Re: Network shutdown under load

[RW]

Thanks for the patch! It seems to solve the problem that
under load (> 50 MBit/s) the network goes down. I've applied
the patch to KVM 0.12.2 running Gentoo. Host and guest is running
kernel 2.6.32 currently (kernel 2.6.30 in guest and 2.6.32 in
host works also for us).

Another host doing the same jobs with the same amount of traffic
and configuration but with KVM 0.11.1 was shutting down
the network interface every 5-10 minutes today while the
patched 0.12.2 was running fine. During the time the 0.11.1 KVMs
were down the patched one delivered >200 MBit/s without
problems. Now both hosts running with the patched
version. We're expecting much more traffic tomorrow so if the
network is still up on thursday I would say the bug is fixed.

Thanks for that patch! It really was a lifesaver today :-)

- Robert


On 02/08/2010 05:10 PM, 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 <toml@us.ibm.com>
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
>
>  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
>   

[Qemu-devel] Re: Network shutdown under load

[Anthony Liguori]

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<toml@us.ibm.com>
> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
>    

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
>
>    

Re: [Qemu-devel] Network shutdown under load

[Lothar Behrens]

Hi,

as I have read that the bug has been fixed, when would it available as  
a new release for the public or at least as a RPM for openSuSE 11.1?

Or is it better to build one myself?

What I also have encountered is that some java code would bring the  
qemu process into a race condition one could probably solve by a sigstop
and then a sigcont.

Is there any relation to this network shutdown bug?

Thanks

Lothar

-- | Rapid Prototyping | XSLT Codegeneration | http://www.lollisoft.de
Lothar Behrens
Heinrich-Scheufelen-Platz 2
73252 Lenningen