|   xen-users
[Xen-users] Re: Xen is a feature 
| To: | Bill Davidsen <davidsen@xxxxxxx> |  
| Subject: | [Xen-users] Re: Xen is a feature |  
| From: | Thomas Gleixner <tglx@xxxxxxxxxxxxx> |  
| Date: | Wed, 3 Jun 2009 22:20:02 +0200 (CEST) |  
| Cc: | ksrinivasan <ksrinivasan@xxxxxxxxxx>, "jeremy@xxxxxxxx" <jeremy@xxxxxxxx>,	"xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>,	"wimcoekaerts@xxxxxxxxxxxx" <wimcoekaerts@xxxxxxxxxxxx>,	"gregkh@xxxxxxx" <gregkh@xxxxxxx>,	George Dunlap <george.dunlap@xxxxxxxxxxxxx>,	"kurt.hackel@xxxxxxxxxx" <kurt.hackel@xxxxxxxxxx>,	"x86@xxxxxxxxxx" <x86@xxxxxxxxxx>,	Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>,	"linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>,	"xen-users@xxxxxxxxxxxxxxxxxxx" <xen-users@xxxxxxxxxxxxxxxxxxx>,	Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>,	Stephen Spector <stephen.spector@xxxxxxxxxx>,	"avi@xxxxxxxxxx" <avi@xxxxxxxxxx>,	"EAnderson@xxxxxxxxxx" <EAnderson@xxxxxxxxxx>,	jens.axboe@xxxxxxxxxx, "mingo@xxxxxxx" <mingo@xxxxxxx>,	"torvalds@xxxxxxxxxxxxxxxxxxxx" <torvalds@xxxxxxxxxxxxxxxxxxxx>,	David Miller <davem@xxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx> |  
| Delivery-date: | Thu, 04 Jun 2009 02:18:57 -0700 |  
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| On Wed, 3 Jun 2009, Bill Davidsen wrote:
> Thomas Gleixner wrote:
> > Aside of the paravirt, which seems to expand through arch/x86 like a
> > hydra, the new patches sprinkle "if (xen_...)" all over the
> > place. These extra xen dependencies are no improvement, they are a
> > royal pain in the ... They are sticky once they got merged simply
> > because the hypervisor relies on them and we need to provide
> > compatibility for a long time.
> > 
> Wait, let's not classify something as "no improvement" when you mean "I don't
> need it."
It's not about "I don't need it.". It's about having Xen dependencies
in the code all over the place which make mainatainence harder. I have
to balance the users benefit (xen dom0 support) vs. the impact on
maintainability and the restrictions which are going to be set almost
in stone by merging it.
> Let's stick to technical issues, and not deny that there are a number of users
> who really will have expanded capability. The technical points are valid, but
> as a former and probable future xen (CentOS) user, so are the benefits.
Refusing random "if (xen...)" dependencies is a purely technical
decision. I have said more than once that I'm not against merging dom0
in general, I'm just frightened by the technical impact of a defacto
ABI which we swallow with it.
We have enough problems with real silicon and BIOS/ACPI already, why
should we add artifical and _avoidable_ virtual silicon horror ?
Thanks,
        tglx
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