Re: [win-pv-devel] Problems with network using 8.2.0.x on Windows 2012R2 and Xen 4.8.1-pre

[Adam Goryachev <mailinglists@xxxxxxxxxxxxxxxxxxxxxx>]

On 26/4/17 18:29, Paul Durrant wrote:
> > -----Original Message-----
> [snip]
> > Hi,
> > I've been using xen for a number of years with a dozen windows 2012R2
> > servers, and have been using one of the ejb drivers. I'm not upgrading
> > to a new version of Xen from Debian testing packages, and having some
> > problems to get the network interface working reliably. To get to this
> > point, I've followed these steps:
> > 1) snapshot the VM drive
> > 2) boot the VM on the new xen platform
> > 3) allow windows to fail to boot (can't find the HDD), boot into
> > recovery menu
> > 4) Boot into safe mode, uninstall the old drivers using an old uninstall
> > script for GPLPV v10
> > 5) Install the new 8.2.0.x drivers
> > 6) Reboot after all drivers are installed
> > 7) Everything works, except the network card which has the yellow ! mark
> > in device manager
> >
> > After numerous attempts to fix this, I can see the following "minimal"
> > steps will give a working device (until the next reboot):
> > 1) Disable the non-working device
> > 2) Enable the device
> > Now, everything works as normal, but as noted, after a reboot it fails
> > to start again.
> >
> > I've managed to enable debugging, and capture the bootup process, then
> > below that is the log of what happens when I disable, and then enable
> > the device. Apologies, but I've trimmed the logs to what I hope is the
> > required information, please let me know if you need more.
> Hi Adam,
>
>    Your problem is this:
>
> 3677@1493170121.472062:xen_platform_log xen platform:
> XENBUS|GnttabExpand: fail1 (c000009a)
>
>    Something has swallowed most of your grant table. I suspect it is your 
> storage interface... Unfortunately blkback has some rather bad defaults and you 
> end up using multiple queues, with multiple pages per queue, and this takes a 
> lot of grant entries. Try reducing to a single page per queue (IOW set 
> blkback's 'max_ring_page_order' to 0) and see if that helps. An alternative 
> would be boot Xen with a larger grant table size... E.g. I boot mine with 
> 'gnttab_max_frames=128' (the default being 32).
>    The fact that you can get the network interface up and running after boot is 
> probably merely because there is less going on storage-wise and you're getting 
> lucky.
Thank you so much Paul, I added the gnttab_max_frames=128 to my grub 
config, and the network will now start automatically with bootup of the 
domU.
Three questions if you could please answer for me:
1) Is there any downside to increasing the value from the default 32 to 
128? Is it just a little extra RAM usage or something? Or is there some 
other problem it might cause?
2) I was concerned that limiting the blkback might slow down the 
performance of that. I don't mind allocating additional RAM to solve 
problems, or to improve performance.
3) If I tried to start multiple domU's on this same dom0, would I end up 
running out, even though I've increased it? Would I run out when trying 
to start the 4th domU?
Regards,
Adam

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