Re: [Xen-users] Debian XenSpecificGlibc

[Ralph Passgang <ralph@xxxxxxxxxxxxx>]

Am Dienstag, 21. März 2006 18:10 schrieb Dirk H. Schulz:
> Mark Petersen schrieb:
> > Has anyone successfully built a debian package with the necessary
> > glibc changes?  I created a dpatch and modified the cflags, but ran
> > into some weirdness.  Then I realized I needed gcc-3.4 so I got a
> > backport gcc-3.4, but now there are some compile errors.  So before I
> > go crazy trying to make this package build, I thought I would check
> > and see if anyone else has tried.  I know lots of people use Debian
> > for their DomU's, someone else must want a proper libc as well.
>
> Why would I want a specialized glibc? What is wrong with the standard one?
>
> Dirk

first of all, this is only interessting for i386. amd64 (and probably other 
architectures) doesn't have this problem at all.

With the std. libc6 package you need to move /lib/tls away on i386 xen hosts, 
because otherwise you would loose a lot of performance. I think every user 
already saw xen warning about that at boot time.

but moving /lib/tls away is not optimal for more than one reason:
- it's no permanent solution. You have to do this after each glibc upgrade on 
each dom0 and domU.
- if you switch a lot between a non-xenified kernel and the xen 
hypervisor+kernel you will end up in moving the /lib/tls directory a lot.
- moving /lib/tls away disabled more features than needed. java and some other 
programs will lose performance because of /lib/tls is missing completly.
- this solution isn't user-friendly at all.

With the glibc packages by Aurelien Jarno (part of the official debian-glibc 
team) all these problems will be fixed.

You have to install "libc6-xen" once, but afterwards never need to take care 
of this again.

- if no xen kernel is running the default libc6 is used like libc6-xen never 
had been installed.
- when a xen kernel is running then the xen optimized version is used for 
optimal performance without the user have to do something. with this special 
libc6 package java, mysql and other applications should benifit and have a 
better performance
- this setup will not break on libc6 upgrades
- it works in dom0 and domU's.
- this solution will be "officially" supported by debian (if xen3 and these 
packages are officially released in debian). you can fill bug reports if 
something is not working as expected...

I think (if no big problems are found) this will go in debian unstable with 
the next glibc upgrade.

But for now, these libc6 packages are not tested! Everybody may use them, but 
without any promise that it is really working as expected... Some team 
members of the pkg-xen debian group (including me) will test these libc6 
packages in the next days.

--Ralph

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