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

[Jakub Kulesza <jakkul@xxxxxxxxx>]

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?

[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.

>
> > 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 :)

>
> > 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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