RE: [Xen-devel] xen and latency - sending faxes via capi (fritzcard USBin domU)

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> I am having the following problem: I am sending faxes via HylaFax over
a
> FritzCard USB in a domU. The Card is attached to an USB controller,
which
> is passed to the domU.
> 
> I had the bvt scheduler, and had no Problems with it. I switched to
the
> credit scheduler a few weeks ago. Now I have the problem, that
sometimes
> faxes don't get transmitted complete.
> 
> The box has a very low load - none of the domains has much to do, and
it is
> a dual Opteron. Sending faxes is time critical - AVM implements the
capi in
> the kernel space, to have lower latency.
> 
> I know, that virtualization is very bad for latency critical tasks.
> 
> I tried to set the weigh of the fax sending domain to a very high
level
> (4000) and the other domains to 128, but it didn't help.
> 
> How can I grant a given latency to a domU? Or yould it be best, to put
the
> capi stuff in dom0? I don't like to put this into dom0, because
rebooting
> dom0 is much more difficult, than domU.

What version of xen are you running?
It might be worth confirming that it's scheduling issues causing the
problem by arranging to pin your domains' VCPUs such that the fax domain
is guaranteed a physical CPU to itself. 

It also might be worth trying latest xen-unstable as there have been a
few minor fixes to the credit scheduler since 3.0.3-0 that might effect
this scenario.

Ian 




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