Re: [win-pv-devel] xenvbd (8.x) - blkback/tapdisk3 problems

[Martin Cerveny <martin@xxxxxxxxx>]

Hello.

On Mon, 31 Oct 2016, Paul Durrant wrote:

> > -----Original Message-----
> > From: Martin Cerveny [mailto:martin@xxxxxxxxx]
> > Sent: 30 October 2016 12:18
> > To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> > Cc: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> > Subject: RE: [win-pv-devel] xenvbd (8.x) - blkback/tapdisk3 problems
> >
> > Hello.
> >
> > Thanks, for response.
> >
> > On Fri, 28 Oct 2016, Paul Durrant wrote:
> > > > -----Original Message-----
> > > > I have problems with xenvbd (8.x). There was NOT problem with older pv-
> > > > drivers xenvbd (7.2x).
> > > > Questions @ bottom.
> > > >
> > > > I use remote raw disk as source (multipath+iscsi+iser+ib).
> > > > Two configs:
> > > >
> > > > --------------------------
> > > >
> > > > 1) use direct blkback (format=raw, vdev=hda, access=rw,
> > > > target=/dev/mapper/3600144f07a0542580000568ba94a0001)
> > > >
> > > > Performance is good, but __unusable__ for working.
> > > >
> > > > Every few seconds/minutes (randomly, depends on disk load) the
> > windows
> > > > hung on io-operations. I usually saw this more often during write
> > operations.
> > > > Sometimes (1:10) I saw "PdoReset" in "DebugView" (DomU):
> > > >
> > > > 00003034        10:12:32        XENVBD|__PdoReset:Target[0] ====>
> > > > 00003054        10:12:53        XENVBD|__PdoReset:Target[0] <====
> > > >
> > > > There is also restart log in Dom0, but no errors on disks/iscsi:
> > > >
> > > > [ 3919.034421] xen-blkback:backend/vbd/3/768: prepare for reconnect
> > > > [ 3919.039869] xen-blkback:ring-ref 32, event-channel 40, protocol 1
> > (x86_64-
> > > > abi)
> > > Yes, XENVBD is being asked to reset because Windows thinks the storage
> > > is stalled and it looks like it was probably right. Suggests a loss of
> > > event notification somewhere.
> > Ok, I suppose Dom0 logs are result of DomU reset, no problem.
> >
> > > > Enviroments:
> > > > - Windows7 x64
> > > > - tested signed winpv drivers 8.1 and primary on development drivers 8.2
> > > > - xen 4.5.3, 4.6 and primary 4.7.0
> > > > - kernels "XenServer" - kernel-3.10.41-353.380450 (and others from XS6.5)
> > > > and kernel-3.10.96-495.383045.x86_64 (and others from XS7)
> > > > - blktap3 - blktap-3.0.0.xs1001-xs6.5.0 and blktap-3.2.0.xs1087-
> > xs7.0.0.x86_64
> > > > ---------------------
> > > >
> > > > Questions:
> > > >
> > > > What is buggy in "direct blkback" chain ?
> > > No idea. Possibly blkback, possibly the underlying storage. Your kernels are
> > old and blkback has undergone many changes in more recent kernels.
> >
> > (I suppose that XS-kernel is super-tuned for Dom0 and there won't be such
> > problem).
> >
> > Now updated Dom0:
> > - fedora 24 + update
> > - kernel - 4.7.9-200.fc24.x86_64
> > - xen 4.7.0 + some backports from XS
> >
> > The problem is the same.
> > When were "changes" to blkback applied ?
> Clearly a 4.7 kernel is about as up-to-date as you want and I am not aware of 
> any changes in blkback since then so it does tend to suggest the problem is 
> elsewhere. It could well be that XENVBD has some bad interaction with 
> blkback... In my test environments I normally use QEMU qdisk as a backend. Do 
> you see the same issues if you, say, point blkback at a loopback file mount or 
> even an nbd device?
Ok. I will prepare and test and debug more in next weeks.

> > > > Was it tested ?
> > > By XenServer? No. XenServer makes no use of blkback.
> > :-((( (I see few patches to blkback (https://github.com/xenserver/linux-
> > 3.x.pg/tree/master/master))
> Well I exaggerated... We need it for corner cases (e.g. early HVM guest boot 
> where QEMU is emulating h/w), but none of the 'official' XenServer SRs will use 
> it once PV drivers are up and running in the guest; the frontends talk straight 
> to tapdisk3 in userspace.
:-)

Thanks, Martin

>  Paul
> > Thanks for answers or hints, Martin Cerveny
> > >  Paul
> > > > Thanks for answers, Martin Cerveny
> > > >
> > > > _______________________________________________
> > > > win-pv-devel mailing list
> > > > win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> > > > https://lists.xenproject.org/cgi-bin/mailman/listinfo/win-pv-devel
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