[Spice-devel] troubleshooting performance and latency issues?

[Frediano Ziglio]

> 
> 
> 
> On 02/05/17 15:22, Frediano Ziglio wrote:
> >>
> >>
> >>
> >> Hi,
> >>
> >> I've observed some latency issues, for example, changing focus from one
> >> terminal to another is a bit sluggish.  Typing isn't too bad.
> >> Interaction with the sliding GNOME unlock screen and drawing the desktop
> >> after unlock is painfully slow.
> >>
> > 
> > Looks like your problems are due to a low bandwidth instead of high
> > latency. Does spice detect a low bandwidth (should be written in the logs)
> > ?
> > 
> 
> Can you suggest which log file to check, or journalctl and a possible
> grep command?
> 

They are in /var/log/libvirt/qemu (at least on my machines).
Should not be big to require a grep, unless you enable additional
logs.

> 
> >> The virtual server I connect to runs Debian jessie and GNOME 3 desktop,
> >> it is a default install:
> >> Xorg = 2:1.16.4-1
> >> xserver-xorg-video-qxl = 0.1.1-2+b1
> >> spice-vdagent = 0.15.0-1.2
> >>
> >> I'm monitoring the latency of the connection to the KVM/libvirt/SPICE
> >> server with Smokeping, average ping time is about 0.8ms, no packet loss.
> >>
> > 
> > With such network latency you should not have much network latency
> > issues, unless ssh (which seems you are using add a lot of it) add this
> > issue.
> > 
> >>
> >> I've setup the KVM/libvirt/SPICE host like this:
> >> Debian stretch
> >> Kernel = 4.9.13
> >> libspice-server1 = 0.12.8-2.1
> >> libvirt0 = 3.0.0-3
> >>
> >>
> >> I've tried using both virt-manager and virt-viewer as clients on a
> >> Debian jessie system, connecting over SSH to the KVM host, these are the
> >> client versions:
> >>
> >> virt-manager = 1:1.0.1-5
> >> virt-viewer = 1.0-1
> >>
> > 
> > Can you try without SSH?
> > 
> 
> OK, I tried this:
> 
>   virsh edit <domain>   and changed the listen IP to 0.0.0.0
> 
> Then I used spicy to connect directly to the port as I wasn't sure how
> to tell virt-manager or virt-viewer to connect directly to the SPICE port.
> 
> I found some things are a bit faster but it is still not ideal
> 
> In particular, rendering the gray background of the GNOME unlock screen
> appears very slow, it renders one line at a time from top to bottom, it
> takes several seconds.  Rendering the desktop background image (default
> Debian theme) was also slow.  I understand that I could change the
> background image, but the gray lock screen, being a single colour,
> shouldn't that render more quickly?
> 

weird, looks like is not compressing at all!
With remote-viewer you can add options like --spice-preferred-compression=glz
(see "remote-viewer --help-spice" command), you should be able to connect
with "remote-viewer spice://<ip>:<port>" (not using ssh).

> Unfortunately, before I could test it more, Xorg crashed again, I've
> submitted the core dump now.
> 
> >> I noticed it appears a little better with virt-manager than virt-viewer,
> >> should there be any difference between these two products if they both
> >> use the same protocol?
> >>
> > 
> > Maybe is due to some compression settings difference. Not sure which
> > compression algorithms are used by virt-manager/virt-viewer.
> > 
> >> Can I do anything to tweak the .ssh/config to make it better?  It
> >> occurred to me that adding "IPQoS lowdelay" might be useful as it
> >> defaults to "throughput" for non-interactive connections.  Maybe
> >> virt-manager should add that on the ssh command line?
> >>
> > 
> > display requires quite lot of bandwidth, if you set network to
> > low delay but you use a lot of bandwidth you'll get worst performance.
> > 
> >> Is there any way to see SPICE latency statistics in the virt-manager GUI?
> >>
> >> Would any other SPICE viewer make a difference?
> >>
> >> Are there any changes I should make to the GNOME desktop configuration
> >> to make it work better through SPICE?  I've heard people comment on
> >> changing to fvwm.
> >>
> >> Can anybody make any other suggestions?
> >>
> >> Regards,
> >>
> >> Daniel
> > 
> > Frediano
> > 
>