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Re: [Xen-users] PCI passthrough partial success

Subject: Re: [Xen-users] PCI passthrough partial success
From: Andy Burns <lists.xensource.com@xxxxxxxxxxxxxx>
Date: Thu, 03 Jul 2008 23:22:50 +0100
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On 02/07/2008 23:27, Christopher Isip wrote:

I have mythbackend running in an Ubuntu-Hardy domU with a Centos 5.1 dom0. Here are the settings that work for me:

I found a bug in the saa7123 tuner driver where it was mapping too large an mmio area, so patched that, then found it was sharing an interrupt with devices from dom0, so added pollirq, now I have an infrequent DMA panic.

    kernel /boot/xen.gz-3.2 swiotlb=256 noirqdebug

I had been searching around for swiotlb info, I'll try your settings tomorrow ...

is noirqdebug preferred instead of pollirq? I was getting the "nobody cared, IRQ disable dmesg"

extra = "swiotlb=force

hmm, my domU kernel crashed immediately when I trye swiotlb=force

#It probably wont hurt to increase the domU's scheduling priority, run this in dom0:

xm sched-credit -d Ubuntu-Mythtv -w 512

So far I've not noticed performance being a problem, recording 3 concurrent streams from a single tuner takes under 10% of one core of a Q9450 cpu.

I would suggest having the Mythtv backend not do any transcoding or commflagging. Instead, create slave mythtv backends without tuners and have them do the transcode and commflagging. This effectively compartmentalizes the commflagger and transcoder so that the main mythtv backend will not drop frames when writing to the disk.

Good suggestion, though again I've been amazed how much faster this backend is at transcoding than my "old" P4 combined frontend/backend.

My only problem with the system is I get dma timeout errors in dmesg. These were present even in a nonxen setup, so I think it is related to my hardware and ivtv.

hmm, mine are panics, not just dmesg, but I never saw them when the tuners were in the non-xen machines.

Hope that helps. I am still trying to find ways to optimize the mythbackend domU so If you have any ideas, please let me know.

Thanks,  will do.

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