Re: [Xen-devel] Radical proposal v2: Publish Amazon's verison now, Citrix's version soon

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 11 Jan 2018, Jan Beulich wrote:
> >>> On 10.01.18 at 18:25, <sstabellini@xxxxxxxxxx> wrote:
> > On Wed, 10 Jan 2018, George Dunlap wrote:
> >> * Executive summary
> >> 
> >> - We've agreed on a "convergence" point for PV shim functionality that
> >>   covers as many users as possible:
> >>  - 'HVM' functionality: boots in HVM mode, has support for Xen 3.4
> >>    event channels, &c, booted via 'sidecar'
> >>  - 'PVH' functionality: boots in PVH mode, booted via toolstack
> >>    changes
> >> 
> >> - "Vixen" (the Amazon shim) and PVH shim (mostly developed by Citrix)
> >>   each cover some users and not others; neither one (yet) covers all
> >>   users
> > 
> > Sorry for being punctilious, but neither one can cover all users: there
> > are users without VT-x on their platform, and both approaches require
> > VT-x.
> 
> For the record, yesterday I've decided to make an attempt to
> create a very simplistic patch to deal with the issue in the
> hypervisor, ignoring (almost) all performance considerations
> (not all, because I didn't want to go the "disable caching" route).
> I've dealt with some of the to-be-expected early bugs, but I'm
> now debugging a host hang (note: not a triple fault apparently,
> as the box doesn't reboot, yet triple faults is what I would have
> expected to occur if anything is wrong here or missing).
> 
> I know that's late, and I have to admit that I don't understand
> myself why I didn't consider doing such earlier on, but the
> much increased pressure to get something like the shim out,
> which
> - doesn't address all cases
> - requires changes to how VMs are being created (which likely will
>   be a problem for various customers)
> - later will want those changes undone
> plus the pretty obvious impossibility to backport something like
> Andrew's (not yet complete) series to baselines as old as 3.2
> made it seem to me that some (measurable!) performance
> overhead can't be all that bad in the given situation.

Thank you for giving it a look! I completely agree with you on these
points. I think we should approach this problem with the assumption that
this is going to be the only long term solution to SP3, while Vixen (or
PVshim) incomplete stopgaps for now.

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