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

[Jakub Kulesza <jakkul@xxxxxxxxx>]

Well, this turns out strange. It is not better but went worse.

Atto provides such results: https://imgur.com/gallery/D4erdER
So it's on par to 8.2.1 with gnttab at 32. But the stability is worse
then before.

Settings from kernel:
# cat /sys/module/xen_blkback/parameters/*
0
1024
1056
1
1
pt., 28 wrz 2018 o 16:04 Paul Durrant <Paul.Durrant@xxxxxxxxxx> napisał(a):
>
> > -----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



-- 
Pozdrawiam
Jakub Kulesza

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