Re: strange guest slowness after some time

["David S. Ahern" <daahern@cisco.com>]

David S. Ahern wrote:
> 
> Rusty Russell wrote:
>> On Wednesday 18 March 2009 16:59:36 Avi Kivity wrote:
>>> Tomasz Chmielewski wrote:
>>>> virtio_net virtio0: id 64 is not a head!
>> This means that qemu said "I've finished with buffer 64" and the guest didn't
>> know anything about buffer 64.
>>
>> We should not lock up, tho networking is toast: I think that qemu got upset
>> and that caused this as well as it to chew 100% cpu.
>>
>> I'll see if I can reproduce with kvm-84 userspace and 2.6.27 guests, 32-bit
>> guests on a 64-bit AMD host.  What's your kvm/qemu command line?
>>
> 
> I've hit this as well.
> 
> Intel host, running RHEL5.3, x86_64 with KVM-81.
> 
> Guest is RHEL4.7, 32-bit, with the virtio drivers from RHEL4.8 beta.
> 
> Happens pretty darn quickly for me.
> 
> david
> 

Like I said, pretty darn quickly.

More information for you. Command line (a few elements blurred) for this
run (started about 15 minutes ago):

kvm -localtime -no-reboot -m 3584 -smp 4 \
-drive file=/dev/cciss/c0d0,if=scsi,cache=off,boot=on \
-drive file=/dev/cciss/c0d1,if=scsi,cache=off,boot=off \
-net nic,vlan=0,macaddr=00:11:22:33:44:55,model=virtio \
-net tap,vlan=0,ifname=tap0,script=no,downscript=no \
-net nic,vlan=1,macaddr=00:12:34:56:78:1,model=virtio \
-net tap,vlan=1,ifname=tap1,script=no,downscript=no \
-usb -usbdevice tablet -mem-path /hugepages \
-pidfile /tmp/1.pid \
-monitor unix:/tmp/1,server,nowait  \
-vnc :1

It does not take much network traffic for the network to lock up. In
this case, the host shows 2 kvm threads spinning -- for vcpus 2,3. I
have vcpus pinned to pcpus (vcpu0:pcpu0, etc).

Backtrace for kvm, though nothing interesting:

Thread 5 (Thread 0x43344940 (LWP 3153)):
#0  0x00002b8af5088c77 in ioctl () from /lib64/libc.so.6
#1  0x0000000000530ece in kvm_run ()
#2  0x0000000000506529 in kvm_cpu_exec ()
#3  0x00000000005067c0 in ap_main_loop ()
#4  0x00002b8af46aa367 in start_thread () from /lib64/libpthread.so.0
#5  0x00002b8af50900ad in clone () from /lib64/libc.so.6

Thread 4 (Thread 0x43d45940 (LWP 3154)):
#0  0x00002b8af5088c77 in ioctl () from /lib64/libc.so.6
#1  0x0000000000530ece in kvm_run ()
#2  0x0000000000506529 in kvm_cpu_exec ()
#3  0x00000000005067c0 in ap_main_loop ()
#4  0x00002b8af46aa367 in start_thread () from /lib64/libpthread.so.0
#5  0x00002b8af50900ad in clone () from /lib64/libc.so.6



In the guest, I see 2 threads of 2 separate processes spinning on cpus
2,3. They appear to be spinning kernel side.

Attempts to restart the network froze the guest console, and at this
point the host shows 3 threads spinning away, though not at 100% cpu.
The qemu monitor was able to push a system_powerdown event to the guest,
and it showed signs of receiving it though it did not powerdown on its own.

david



> 
>> Thanks,
>> Rusty.
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>