Xen users - May 2008 - Re: calculating the needed swiotlb in dom0

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


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On Wed, May 28, 2008 at 8:30 AM, Christopher Isip <cmisip@gmail.com>
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


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On Wed, May 28, 2008 at 11:14 PM, Christopher Isip <cmisip@gmail.com>
wrote:
>
>
> On Wed, May 28, 2008 at 8:30 AM, Christopher Isip <cmisip@gmail.com>
> 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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