Re: [win-pv-devel] Windows on Xen bad IO performance

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Paul Durrant
> Sent: 28 September 2018 15:04
> To: 'Jakub Kulesza' <jakkul@xxxxxxxxx>
> Cc: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: RE: [win-pv-devel] Windows on Xen bad IO performance
> 
> > -----Original Message-----
> > From: Jakub Kulesza [mailto:jakkul@xxxxxxxxx]
> > Sent: 28 September 2018 13:51
> > To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> > Cc: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> > Subject: Re: [win-pv-devel] Windows on Xen bad IO performance
> >
> > pt., 28 wrz 2018 o 14:00 Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> > napisał(a):
> > [cut]
> >
> > > > >   Also the master branch should default to a single (or maybe 2?)
> > page
> > > > ring, even if the backend can do 16 whereas all the 8.2.X drivers
> will
> > use
> > > > all 16 pages (which is why you need a heap more grant entries).
> > > > >
> > > >
> > > > can this be tweaked somehow on current 8.2.X drivers? to get a
> single
> > > > page ring? max_ring_page_order on xen_blkback in dom0?
> > >
> > > Yes, tweaking the mod param in blkback will do the trick.
> > >
> > > >
> >
> > Current debian defaults are:
> > log_stats=0
> > max_buffer_pages=1024
> > max_persistent_grants=1056
> > max_queues=4
> > max_ring_page_order=4
> >
> > what would you tweak? max_queues and max_ring_page_order to 1?
> 
> 1 will give you a 2 page ring, which should be fine.

Sorry.. should have said set max_queues to 1 too. Multi-queue isn't that much 
use yet.

  Paul

> 
> >
> > [cut]
> > > > >   You could try setting up a logo kit yourself and try testing
> > XENVBD to
> > > > see if it passes... that would be useful knowledge.
> > > >
> > > > seems fun. Where can I read on how to set up the logo kit?
> > > >
> > >
> > > See https://docs.microsoft.com/en-us/windows-
> hardware/test/hlk/windows-
> > hardware-lab-kit
> > >
> > > > Is there an acceptance testplan that should be run?
> > > >
> > >
> > > I've not use the kit in a while but I believe it should automatically
> > select all the tests relevant to the driver you elect to test (which is
> > XENVBD in this case).
> >
> > I will read and see what I can do about this. I can sacrifice a few
> > evenings for sure.
> >
> 
> Cool.
> 
> > >
> > > > Is there a list of issues that you'll want to get fixed for 9.0? Is
> > > > Citrix interested right now in getting Windows VMs of their
> customers
> > > > running better :)?
> > >
> > > Indeed Citrix should be interested, but testing and updating the
> branded
> > drivers has to be prioritized against other things. Whether Citrix wants
> > to update branded drivers does not stop me signing and releasing the Xen
> > Project drivers though... it just means they won't get as much testing,
> so
> > I'd rather wait... but only if it doesn't take too long.
> >
> > ech, priorities, resources, deadlines. I'll hook you up on Linkedin :)
> >
> 
> :-)
> 
> Cheers,
> 
>   Paul
> 
> > >
> > > > Testing windows VMs on VMware the same way (with
> > > > VMware's paravirtual IO) is not stellar anyway, looks crap when you
> > > > compare it to virtio on KVM. And 9.0-dev I'd say would be on par
> with
> > > > the big competitor.
> > > >
> > > > Funny story, I've tried getting virtio qemu devices running within a
> > > > XEN VM, but this is not stable enough. I have managed to get the
> > > > device show up in Windows, didn't manage to put a filesystem on it
> > > > under windows.
> > > >
> > >
> > > A lot of virtio's performance comes from the fact that KVM is a type-2
> > and so the backend always has full privilege over the frontend. This
> means
> > that QEMU is set up in such a way that it has all of guest memory mapped
> > all the time. Thus virtio has much less overhead, as it does not have to
> > care about things like grant tables.
> >
> > clear.
> >
> > --
> > Pozdrawiam
> > Jakub Kulesza
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