(In reply to comment #0)
> I tried to generate a debug log by running this command:
> virt-top --debug virt-top.log
> 
> When I do that, virt-top runs normally.
> After exiting virt-top, the debug file is empty.  It is created
> by the program so it is doing something. 

That's good, because it means nothing is writing errors to stderr
which are being lost.

However for this I'd also like to see libvirt debugging, so can
you do:

export LIBVIRT_DEBUG=1
virt-top --debug virt-top.log

and append the log file here.

Created attachment 418641 [details]
Log with libvirt debugging

Same here, RDRQ WRRQ RXBY TXBY empty with 1.0.4 (not empty with 0.3.3.1).

What's the output of virsh *stat commands, and virt-top --debug?  (see
comment 0 and comment 1).

Same problem here.

[root@r210xen ~]# virsh dumpxml rhel55pv
<domain type='xen' id='3'>
  <name>rhel55pv</name>
  <uuid>2a616433-9be9-6a0b-8bb4-af780570b41f</uuid>
  <memory>524288</memory>
  <currentMemory>524288</currentMemory>
  <vcpu>1</vcpu>
  <bootloader>/usr/bin/pygrub</bootloader>
  <os>
    <type>linux</type>
    <kernel>/var/lib/xen/boot_kernel.E1DT0X</kernel>
    <initrd>/var/lib/xen/boot_ramdisk.kFPrQz</initrd>
    <cmdline>ro root=/dev/VolGroup00/LogVol00</cmdline>
  </os>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <disk type='block' device='disk'>
      <driver name='phy'/>
      <source dev='/dev/VolGroup01/rhel55pv'/>
      <target dev='xvda' bus='xen'/>
    </disk>
    <interface type='bridge'>
      <mac address='00:16:36:65:e2:2f'/>
      <source bridge='xenbr0'/>
      <script path='vif-bridge'/>
      <target dev='vif3.0'/>
    </interface>
    <console type='pty' tty='/dev/pts/1'>
      <source path='/dev/pts/1'/>
      <target port='0'/>
    </console>
    <input type='mouse' bus='xen'/>
    <graphics type='vnc' port='5900' autoport='yes' keymap='en-gb'/>
  </devices>
</domain>

[root@r210xen ~]# virsh domifstat rhel55pv vif3.0
vif3.0 rx_bytes 21124047
vif3.0 rx_packets 45256
vif3.0 rx_errs 0
vif3.0 rx_drop 3703
vif3.0 tx_bytes 482084
vif3.0 tx_packets 1884
vif3.0 tx_errs 0
vif3.0 tx_drop 0

[root@r210xen ~]# virsh domblkstat rhel55pv xvda
xvda rd_req 13822
xvda rd_bytes 229754368
xvda wr_req 7523
xvda wr_bytes 64865280
xvda errs 0

virt-top --debug creates an empty debug file.

I've setup a reproducer, please contact me if you need to access it.

Julio, do the stats change over time, eg. if you run the domifstat
command, wait a minute, then run it again?

Yes, they do:

[root@r210xen ~]# virsh domifstat rhel55pv vif3.0
vif3.0 rx_bytes 25297484
vif3.0 rx_packets 49236
vif3.0 rx_errs 0
vif3.0 rx_drop 3703
vif3.0 tx_bytes 557224
vif3.0 tx_packets 3055
vif3.0 tx_errs 0
vif3.0 tx_drop 0

[root@r210xen ~]# virsh domblkstat rhel55pv xvda
xvda rd_req 19453
xvda rd_bytes 259163648
xvda wr_req 42542
xvda wr_bytes 227656704
xvda errs 0

OK I have a theory about why this is happening now.

If you have EPEL 5, you could try this test ...

# yum install ocaml ocaml-findlib-devel ocaml-libvirt-devel

Copy the following into a file, change the guest and device
if necessary, and make sure the file is chmod +x (executable):

-----------------------
#!/usr/bin/ocamlrun /usr/bin/ocaml
#use "topfind";;
#require "libvirt";;
let guest = "rhel55pv"
let device = "xvda"
open Printf
let conn = Libvirt.Connect.connect_readonly ()
module D = Libvirt.Domain
let dom = D.lookup_by_name conn guest
let { D.rd_req = rd_req; rd_bytes = rd_bytes;
      wr_req = wr_req; wr_bytes = wr_bytes } = D.block_stats dom device
let () =
  printf "rd_req = %Ld  rd_bytes = %Ld\n" rd_req rd_bytes;
  printf "wr_req = %Ld  wr_bytes = %Ld\n" wr_req wr_bytes
-----------------------

sudo /tmp/test.ml

For me, on Fedora, this prints stats, eg:

rd_req = 120013  rd_bytes = 4103219200
wr_req = 37548  wr_bytes = 5163249664

but on RHEL 5 this prints an error:

Exception: Libvirt.Not_supported "virDomainBlockStats".

The good news is that if you can reproduce the same error,
then it's very easy to fix -- just need a simple recompile
against the updated libvirt.

Richard, I can reproduce the same error:

[root@r210xen ~]# /tmp/test.ml 
Exception: Libvirt.Not_supported "virDomainBlockStats".

Richard, this BZ seems to be a duplicate of bz#487533.

*** Bug 487533 has been marked as a duplicate of this bug. ***

I agree.  BTW someone with some spare time can just go ahead
and fix this by rebuilding ocaml-libvirt and virt-top packages.

I can confirm that this works, except that ocaml-libvirt-0.4.1.1 uses bits of libvirt that are deprecated in recent releases, and so can't be compiled with -Wall -Werror. Adding -Wno-deprecated-declarations fixes this.

Created attachment 455851 [details]
Patch to compile ocaml-libvirt with -Wno-deprecated-declarations