Re: [HYBRID]: status update...

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Aug 01, 2012 at 06:51:56PM +0200, Sander Eikelenboom wrote:
> Wednesday, August 1, 2012, 6:21:57 PM, you wrote:
> 
> > On Wed, Aug 1, 2012 at 5:05 PM, Konrad Rzeszutek Wilk
> > <konrad.wilk@oracle.com> wrote:
> >> On Wed, Aug 01, 2012 at 04:59:58PM +0100, George Dunlap wrote:
> >>> On Wed, Aug 1, 2012 at 4:25 PM, Konrad Rzeszutek Wilk
> >>> <konrad.wilk@oracle.com> wrote:
> >>> > On Wed, Aug 01, 2012 at 04:25:01PM +0100, George Dunlap wrote:
> >>> >> I hope this isn't bikeshedding; but I don't like "Hybrid" as a name
> >>> >> for this feature, mainly for "marketing" reasons.  I think it will
> >>> >> probably give people the wrong idea about what the technology does.
> >>> >> PV domains is one of Xen's really distinct advantages -- much simpler
> >>> >> interface, lighter-weight (no qemu, legacy boot), &c &c.  As I
> >>> >> understand it, the mode you've been calling "hybrid" still has all of
> >>> >> these advantages -- it just uses some of the HVM hardware extensions
> >>> >> to make the interface even simpler / faster.  I'm afraid "hybrid" may
> >>> >> be seen as, "Even Xen has had to give up on PV."
> >>> >>
> >>> >> Can I suggest something like "PVH" instead?  That (at least to me)
> >>> >> makes it clear that PV domains are still fully PV, but just use some
> >>> >> HVM extensions.
> >>> >
> >>> > if (xen_pvh_domain()?
> >>> >
> >>> > if (xen_pv_h_domain()?
> >>> >
> >>> > if (xen_h_domain()) ?
> >>> >
> >>> > if (xen_pvplus_domain()) ?
> >>> >
> >>> > if (xen_pv_ext_domain()) ?
> >>> >
> >>> > I think I like 'pv+'?
> >>>
> >>> I could deal with pv+.  However, in general I dislike that kind of
> >>> "now even better!" marketing.  PV+, EPV (Enhanced / extended PV), PVX
> >>> (Extreme PV!) -- they all sound cool when they come out, but five
> >>> years later, when they're not so new or sexy anymore, they all sound
> >>> lame.  PVH is just descriptive -- it will always be PV with HVM
> >>> extensions, so it will age much better. :-)
> >>
> >> How about pv_with_mmu_in_hvm_container_domain() ?
> >>
> >> Ok, that is a bit to lengthy. How about then:
> >>
> >> if (xen_pvhvm_ext_domain()) ?
> >>
> >> The 'if (xen_pvh_domain())' is just one characer short of 'xen_pv_domain()'
> >> and one might not notice it. Perhaps then 'if (xen_pv_h_domain()' ?
> 
> > Hmm -- that's an interesting issue I hadn't thought of.  "PVHVM" has
> > already been sort of taken by Stefano's extensions to allow Linux
> > kernels booted in HVM mode to use some of the PV extensions.  I tend
> > to think "xen_pvh_domain()" is probably OK, but maybe calling it
> > "pvext" (or "pvhext") in the code, and "PVH" in documentation /
> > stories?  Just using "pvext" everywhere could work as well; it's a
> > little bit "now even better!", but not as much as pvplus.
> 
> Am i mistaken in saying that both "Hyrbid" and "PVHVM" are both targeting the same, but approaching it from a different base / direction (PV + HVM extensions versus HVM + PV extensions) ?

Pretty much. HVM is QEMU with emulated devices and then ditching most of them and
turning on PV for everything you can.

PV ext is starting with PV and using the SVM/VMX container (so no QEMU) to deal
with the memory management. The PV functionality is still present except that
MMU operations and syscalls' don't go through the hypervisor anymore.

> If that's the case, how far are these apart from meeting each other in the middle, and what would be the fundamental difference ?

At the end of the day they are pretty similar .. a PVHVM guest tries to
use the least amount of QEMU functionality and use PV drivers. For MMU
and such it uses VMX/SVM container. The PV ext would be using no QEMU
but using VMX/SVM container.
> It seems to be the full qemu container / emulated driver model availability on HVM + PV extensions ?

Sure, that is the big difference - PVHVM needs QEMU to bootup at least.

> 
> Just wondering if the naming should express that most explicit and fundamental difference (if there is one :-) ) ?

"if (xen_fat_domain())' (so QEMU) and 'if (xen_slim__domain())' (no QEMU)?