[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-users] Re: Xen is a feature
* Avi Kivity <avi@xxxxxxxxxx> wrote: > Linus Torvalds wrote: >> The point? Xen really is horribly badly separated out. It gets way more >> incestuous with other systems than it should. It's entirely possible >> that this is very fundamental to both paravirtualization and to >> hypervisor behavior, but it doesn't matter - it just measn that I can >> well see that Xen is a f*cking pain to merge. >> >> So please, Xen people, look at your track record, and look at the >> issues from the standpoint of somebody merging your code, rather >> than just from the standpoint of somebody who whines "I want my >> code to be merged". >> >> IOW, if you have trouble getting your code merged, ask yourself >> what _you_ are doing wrong. > > There is in fact a way to get dom0 support with nearly no changes > to Linux, but it involves massive changes to Xen itself and > requires hardware support: run dom0 as a fully virtualized guest, > and assign it all the resources dom0 can access. It's probably a > massive effort though. > > I've considered it for kvm when faced with the "I want a thin > hypervisor" question: compile the hypervisor kernel with PCI > support but nothing else (no CONFIG_BLOCK or CONFIG_NET, no device > drivers), load userspace from initramfs, and assign host devices > to one or more privileged guests. You could probably run the host > with a heavily stripped configuration, and enjoy the slimness > while every interrupt invokes the scheduler, a context switch, and > maybe an IPI for good measure. This would be an acceptable model i suspect, if someone wants a 'slim hypervisor'. We can context switch way faster than we handle IRQs. Plus in a slimmed-down config we could intentionally slim down aspects of the scheduler as well, if it ever became a measurable performance issue. The hypervisor would run a minimal user-space and most of the context-switching overhead relates to having a full-fledged user-space with rich requirements. So there's no real conceptual friction between a 'lean and mean' hypervisor and a full-featured native kernel. This would certainly be an utterly clean design, and it would be interesting to see a Linux/Xen + Linux/Dom0 combo engineered in such a way - if people really find this layered kernel approach interesting. So the door is not closed to dom0 at all - but it has to be designed cleanly without messing up the native kernel. Ingo _______________________________________________ Xen-users mailing list Xen-users@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-users
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