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[Xen-devel] Xen is a feature

To: Ingo Molnar <mingo@xxxxxxx>
Subject: [Xen-devel] Xen is a feature
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Thu, 28 May 2009 17:45:34 -0700
Cc: Nick Piggin <npiggin@xxxxxxx>, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Wim Coekaerts <wimcoekaerts@xxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxx>, Stephen Spector <stephen.spector@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, "Kurt C. Hackel" <kurt.hackel@xxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx, Avi Kivity <avi@xxxxxxxxxx>, Eric Anderson <EAnderson@xxxxxxxxxx>, Jens Axboe <jens.axboe@xxxxxxxxxx>, Ky Srinivasan <ksrinivasan@xxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Greg KH <gregkh@xxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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Ingo Molnar wrote:
Xen changes - especially dom0 - are overwhelmingly not about improving Linux, but about having some special hook and extra treatment in random places - and that's really bad.

You've made this argument a few times now, and I take exception to it.

It seems to be predicated on the idea that Xen has some kind of niche usage, with barely more users than Voyager. Or that it is a parasite sitting on the side of Linux, being a pure drain.

Neither is true. Xen is very widely used. There are at least 500k servers running Xen in commercial user sites (and untold numbers of smaller sites and personal users), running millions of virtual guest domains. If you browse the net at all widely, you're likely to be using a Xen-based server; all of Amazon runs on Xen, for example. Mozilla and Debian are hosted on Xen systems.

Hardware vendors like Dell and HP are shipping servers with Xen built into the firmware, and increasingly, desktops and laptops. Many laptop "instant-on/instant-access" features are based on a combination of Xen and Linux.

All major Linux distributions support running as a Xen guest, and many support running as a Xen host.

For these users, Xen support is an active feature of Linux; Linux without Xen support would be much less useful to them, and better Xen support would be more useful. For them, Xen support is no different from any other kind of platform support. They are being actively hampered by the fact that the only dom0 support is available in the form of either ancient or very patched kernels.
To them, improved Xen support *is* "improving Linux".

Your view appears to be that virtualization is either useless, or a neat trick useful for doing a quick kernel test (which is why kvm got early traction in this community; it is well suited to this use-case). But that is a very parochial kernel-dev view. For many users, virtualization (in general, but commonly on Xen) has become an absolutely essential part of their computing infrastructure, and they would no more go without it than they would go without ethernet.

We're taking your technical critiques very seriously, of course, and I appreciate any constructive comment. But your baseline position of animosity towards Xen is unreasonable, unfair and unnecessary.


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