[Xen-users] Re: calculating the needed swiotlb in dom0

To:	xen-users@xxxxxxxxxxxxxxxxxxx
Subject:	[Xen-users] Re: calculating the needed swiotlb in dom0
From:	"Christopher Isip" <cmisip@xxxxxxxxx>
Date:	Thu, 29 May 2008 21:18:17 -0400
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On Wed, May 28, 2008 at 11:14 PM, Christopher Isip <cmisip@xxxxxxxxx> wrote:

On Wed, May 28, 2008 at 8:30 AM, Christopher Isip <cmisip@xxxxxxxxx> wrote:
I just found out that setting swiotlb=128 in dom0 grub.conf allowed me to run my mythtv domU with additonal options to ivtv:
in /etc/modprobe.d/options
options ivtv enc_mpg_buffers=8

Setting this to any higher value causes a kernel panic. I want to be able to specify
options ivtv enc_mpg_buffers=16 enc_vbi_buffers=8

How much swiotlb do I need? Is there a way to figure this out or is it just trial and error.

Thanks
Chris

After a bunch of trials, I managed to get mythtv to boot without SW-IOMMU errors and without kernel panic with the ivtv options set at " options ivtv enc_mpg_buffers=16 enc_vbi_buffers=8" . I had to specify on the kernel line in dom0's grub.conf : swiotlb=256 and then in the myth domU's grub.conf : swiotlb=128,force.

It would probably work with the dom0 grub swiotlb set at 128 only although I haven't tried that yet.

Hopefully, this will get rid of a bunch of ivtv buffer errors in dmesg.

Thanks
Chris

Well, this afternoon, I decided to work on the xen server directly instead of using ssh through my laptop. I was suprised to see kernel panics and SW-IOMMU out of space errors again. I tried all different configurations I tried last night to no avail. After about an hour of trying , I thought to myself that the only thing different that I am doing today is that I am not using ssh to connect to the xen server. I went back upstairs and connected through ssh, put in the configurations that I knew worked last night, rebooted, reconnected and restarted the mythtv domU and it worked. I think this is a good bit of information to know that might help anyone else trying to setup a mythtv xen domU. For some reason, logging in to a machine physically, causes the SW-IOMMU space to be used. Perhaps somebody else could enlighten me on what is happening here.

Thanks
Chris

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