Re: [win-pv-devel] Windows 10 domU is unstable with PV Bus Driver

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Michel D'HOOGE [mailto:michel.dhooge@xxxxxxxxx]
> Sent: 05 December 2017 10:31
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [win-pv-devel] Windows 10 domU is unstable with PV Bus Driver
> 
> Hi Paul,
> 
> Here's a late follow-up on my problem…
> 
> 
> > That means libxl should fire up blkback as your backend, in which case you
> may well end up
> > with things like multi-page rings cranked up to the max and indirect
> descriptors turned on.
> > I suggest you turn up the number of grant frames allocated to your guest...
> it may well be
> > running out of grant references which would very much explain your
> stability issues.
> > If you are running a bleeding edge Xen then you can set the number of
> frames on a per-guest basis.
> > If not then you'll need to set it globally on the xen command line
> > (e.g. add gnttab_max_frames=128 to the line).
> 
> So, after upgrading the domU to Win10 rs3, I managed to re-install
> xenvbd and everything was fine for a couple of days.
> Then it hung again and I saw in the logs a lot of lines like:
> XENBUS|RangeSetPop: fail2
> XENBUS|RangeSetPop: fail1 (c000009a)
> GNTTAB: MAP XENMAPSPACE_grant_table[7] @ 00000000.f2008000
> XENBUS|GnttabExpand: added references [00000e00 - 00000fff]
> 
> So I added gnttab_max_frames=128 to my config and everything is fine
> again.
> 

Well, seeing a RangeSetPop: fail2 actually just means a range set it out of 
space. That's why you then see the follow-up GnttabExpand line (because the 
range set in question was the grant table). So, you're likely see a few of 
these sequences but you know things have gone wrong then the number in the 
square brackets on the MAP XENMAPSPACE_grant_table line reaches the limit of 
your grant frames, so I assume you saw it hit 32 before and then everything 
stopped. Setting to 128 should give you enough head-room for a few multi-page 
storage rings and multi-queue networks.

> BTW, what is a "bleeding edge" Xen for you? Because I'm with 4.9 and I
> can't think it is possible to set that on a per-guest basis.
> 

By bleeding edge I mean a recent build of the master branch of xen.git, so a 
4.10 rc as it stands. With such a build you can now set the grant table frame 
limit on a per-guest basis; see 
http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=docs/man/xl.cfg.pod.5.in;hb=HEAD#l533.

> Thanks again
> M.

No problem :-) Cheers,

  Paul
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