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[Fwd: Re: [Xen-devel] Zaptel PCI IRQ problem]

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Subject: [Fwd: Re: [Xen-devel] Zaptel PCI IRQ problem]
From: François Delawarde <fdelawarde@xxxxxxxxxxxxxxxxx>
Date: Mon, 21 May 2007 16:19:35 +0200
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Sorry to insist, but I would really like to be able to use Xen and my zaptel hardware all together in Dom0. I was just wondering if the 3.1 release could contain some changes compared to 3.0.4 related to IRQ handling or scheduling that could workout my problem.



I actually first asked to asterisk mailing lists, and a few persons told me that it was Xen's fault, as it was not yet 'mature' enough to have a good IRQ handling under load.

Note that I made tests the last few days as I wasn't sure if it was Xen or not, and the exact same system works perfectly with a normal Linux kernel (same config file except for Xen stuff that are removed). A Dom-0 kernel without any VMs running comports itself the way I described (bad), and I tried both schedulers (sedf and credit) without success.

It doesn't appear to be a load problem as the load is about the same with the non-Xen kernel I tried, but with IRQ handling in load period. I'm talking about a machine that is certainly not over-loaded, but that once in a while suffers some iowait for disk access. Under Xen kernel, if I kill everything I can and only leave Asterisk with at most one simultaneous conversation, it works quite nice.

I'm using the debian (I think they actually come from fedora) patches for 2.6.18, and just want to know if this issue is known or has/will been/be resolved somehow in future versions, if there is anyway I can deal with it with some kernel configuration, or if I should wait a few months/years more to be able to use Xen in my specific setting.


Ian Pratt wrote:
I'm currently trying to run an Asterisk server in a Xen kernel under
Dom0 (debian kernel 2.6.18 with xen hypervisor 3.0.4). I had read of
some possible timing issues with ztdummy (using rtc) under DomU, but I
have a zaptel compatible PCI card (TDM400P), and I experience big
problems with IRQ misses every time there is a bit of load on the server
(for example, when an HVM DomU is running). The card is supposed to
report 1000 interruptions per second, but it doesn't, and consequences
are horrible crackling sound in communications. Running the utility
zttest to check for the stability of those interrupts under a small bit
of load, i get:

I believe folk have had success running asterisk in a domU and assigning the PCI device directly to the guest. It's best to set the affinity masks for other guests and dom0 such that the domU with asterisk in it has a dedicated physical CPU core.
We ran asterisk on an older version of Xen without any problems, and nothing 
has changed that should effect xen's ability to do this. [you could try using 
the sedf scheduler if you still have problems with 'credit']


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