Xen devel - Jun 2005 - Brief TLS/PAE/xenbus/AGP/Debian/VCS questions

I''ve been away from the Xen land for a while for various reasons. So
I''ve recently skimmed through quite a lot of mails here and
I''m not
sure if I got everything properly.

What''s happending with the TLS issue? Is /lib/tls still harmful? There
was talk of a glibc patch - did that ever progress anywhere? Did
making it work require changes to Xen as well as glibc?

PAE support seems to be progressing nicely. Great work! Some mails
seem to be saying matter of factly that it will be in Xen 3.0 - this
is great news.

There are news of AGP/DRM fixes in 2.0.6. Last time my nForce2 chipset
fell over by the lack of secondary devices (the bridges) as they were
hidden by Xen. I guess this is still the case in 2.0. Is the new
PCI/ACPI/etc. code now in unstable? Does that mean that the bridge
devices should now show up normally and I could new try to get AGPGART
support working?

How far along is xenbus right now? I''m particularily interested in a
local communication channel between domain 0 and other domains that
would not be a network interface. Better console support would be
really nice as well, but in the end that is a secondary concern. What
remains to be done?

Is anyone making Debian packages of the unstable branch code? If not,
I guess I will roll my own. The stable packages are still at 2.0.5 in
the Debian archive, but I guess they will get to 2.0.6 once Adam Heath
gets a breather from his work.

The VCS issue is still open I guess? I''m not allowed to use BitKeeper
anyway, so this is good news to me in a way. But I guess I will keep
on using the nightly source snapshots until a change has been made.

And lastly - roadmap says Xen 3.0 in July - now that would be quite
soon indeed.

That''s it for now. This questionnaire is here just if someone happens
to have the time to fill me in - I will do my own digging if not.

TIA,
-- Naked


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> What''s happending with the TLS issue? Is /lib/tls still harmful?
There
> was talk of a glibc patch - did that ever progress anywhere? Did
> making it work require changes to Xen as well as glibc?
Not harmful but slower.  There is a glibc patch, which you can apply if you 
want (the nicest would be for a distro to ship it).  The glibc people
weren''t
interested in merging it.

Won''t be an issue of x86_64, or any other arch.
> PAE support seems to be progressing nicely. Great work! Some mails
> seem to be saying matter of factly that it will be in Xen 3.0 - this
> is great news.
That''s the plan.
> There are news of AGP/DRM fixes in 2.0.6. Last time my nForce2 chipset
> fell over by the lack of secondary devices (the bridges) as they were
> hidden by Xen. I guess this is still the case in 2.0.
AGP etc should work now (modulo buggy drivers).

bridges still hidden, AFAIK.  see below...
> Is the new 
> PCI/ACPI/etc. code now in unstable? Does that mean that the bridge
> devices should now show up normally and I could new try to get AGPGART
> support working?
Bridges should now appear.
> How far along is xenbus right now? I''m particularily interested in
a
> local communication channel between domain 0 and other domains that
> would not be a network interface. Better console support would be
> really nice as well, but in the end that is a secondary concern. What
> remains to be done?
Getting there.  Grep for XenBus and XenStore in the unstable tree.  Others may 
have mroe precise news.
> Is anyone making Debian packages of the unstable branch code? If not,
> I guess I will roll my own. The stable packages are still at 2.0.5 in
> the Debian archive, but I guess they will get to 2.0.6 once Adam Heath
> gets a breather from his work.
I think a few people had agreed to co-operate to make this happen. 
We''re very
keen to maintain the good support Debian has had for Xen.
> The VCS issue is still open I guess? I''m not allowed to use
BitKeeper
> anyway, so this is good news to me in a way. But I guess I will keep
> on using the nightly source snapshots until a change has been made.
Switching to Mercurial today.  After tomorrow, we''ll never use BK again
:-)
> And lastly - roadmap says Xen 3.0 in July - now that would be quite
> soon indeed.
More like 3.0-testing in July.
> That''s it for now. This questionnaire is here just if someone
happens
> to have the time to fill me in - I will do my own digging if not.
HTH,
Mark
> TIA,
> -- Naked
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
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On Thu, 30 Jun 2005, Mark Williamson wrote:
> > What''s happending with the TLS issue? Is /lib/tls still
harmful? There
> > was talk of a glibc patch - did that ever progress anywhere? Did
> > making it work require changes to Xen as well as glibc?
> 
> Not harmful but slower.  There is a glibc patch, which you can apply if 
> you want (the nicest would be for a distro to ship it).  The glibc 
> people weren''t interested in merging it.
I think the glibc people just created a new glibc variant,
which is in Fedora Rawhide already.


-- 
The Theory of Escalating Commitment: "The cost of continuing mistakes is
borne by others, while the cost of admitting mistakes is borne by
yourself."
  -- Joseph Stiglitz, Nobel Laureate in Economics

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Rik Van Riel wrote:
> On Thu, 30 Jun 2005, Mark Williamson wrote:
>
>>> What''s happending with the TLS issue? Is /lib/tls still
harmful?
>>> There was talk of a glibc patch - did that ever progress anywhere? 
>>> Did making it work require changes to Xen as well as glibc?
>>
>> Not harmful but slower.  There is a glibc patch, which you can
>> apply if you want (the nicest would be for a distro to ship it).
>> The glibc people weren''t interested in merging it.
>
> I think the glibc people just created a new glibc variant,
> which is in Fedora Rawhide already.
I went digging around for the patch and eventually had to a Fedora
glibc source RPM package to find it - is it available in any sane
place?

Compiling with ''-mno-tls-direct-seg-refs'' is still needed as
well I
guess.

So, just to clarify the loose ends.

Using TLS is now perfectly safe, only causes a performance loss? Glibc
is the biggest culprit in losing performance - how much is this in
practise?

Does the patch given fix most of the performance loss, or the compiler
flag given, or are both needed to avoid most of it?

Why would glibc not take it in the standard version, but only a
variant? Is this variant included in the standard glibc distribution
and can it be enabled by some compile option? I would assume there''s a
slight performance degration because of it or something.

Are there any valid reasons for not including that in, say, the
default Debian glibc?

Thanks again, you''ve been very helpful, as always.

-- Naked



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> 
> > Is anyone making Debian packages of the unstable branch code? If not,
> > I guess I will roll my own. The stable packages are still at 2.0.5 in
> > the Debian archive, but I guess they will get to 2.0.6 once Adam Heath
> > gets a breather from his work.
> 
> I think a few people had agreed to co-operate to make this happen. 
We''re very
> keen to maintain the good support Debian has had for Xen.
> 
I believe that Adam Heath doesn''t have the time to maintain the
packages (that was posted to the list a while back). I made public
some packages that I created (for 2.0.6), and have been getting
feedback on them, especially on things such as how the packages are
broken down (slightly differently from the original), how stable are
the modules, how to best deal with the /lib/tls issue (if you get
answers to your most recent questions about it, that would help, too)
and what''s the appropriate behaviour in an "upgrade" on a
machine that
has running domUs.

My intention was to create a set of unstable packages if the stable
packages seemed useful (but that certainly won''t be this week) and
also post (probably to xen-users) again to try to see who else is
still working on this.

Also (if you haven''t seen it) this page has some comments on the
patches/glibc/tls issue a link to a package that somebody built:
http://wiki.xensource.com/xenwiki/DebianSarge

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Yvette Chanco wrote:
>>> Is anyone making Debian packages of the unstable branch code? If
>>> not, I guess I will roll my own. The stable packages are still at
>>> 2.0.5 in the Debian archive, but I guess they will get to 2.0.6
>>> once Adam Heath gets a breather from his work.
>>
>> I think a few people had agreed to co-operate to make this happen.
>> We''re very keen to maintain the good support Debian has had
for
>> Xen.
>
> I believe that Adam Heath doesn''t have the time to maintain the
> packages (that was posted to the list a while back).
The only mail I could find said this:

,----[ From: Adam Heath <doogie@brainfood.com> ]
| I''ve been completely swamped at work.  I''ll make time to
look at them
| this week.
`----
> I made public some packages that I created (for 2.0.6), and have
> been getting feedback on them, especially on things such as how the
> packages are broken down (slightly differently from the original),
> how stable are the modules, how to best deal with the /lib/tls issue
> (if you get answers to your most recent questions about it, that
> would help, too) and what''s the appropriate behaviour in an
> "upgrade" on a machine that has running domUs.
Yeah, I saw them, but didn''t try them yet. My main concern however is
not about getting 2.0.6 Debian packages for myself, but to get them in
the Debian repository.
> My intention was to create a set of unstable packages if the stable
> packages seemed useful (but that certainly won''t be this week) and
> also post (probably to xen-users) again to try to see who else is
> still working on this.
I would love to see a set of regularily updated unstable packages -
they wouldn''t need to be as fancy and fine-grained as the stable
Debian packages, but rather something that would have less of a chance
of requiring changes when the unstable tree gets new features.
> Also (if you haven''t seen it) this page has some comments on the
> patches/glibc/tls issue a link to a package that somebody built:
> http://wiki.xensource.com/xenwiki/DebianSarge
Oh, thanks! Hadn''t even noticed that we had a Wiki yet, let alone one
that contained something useful ;-)

-- Naked


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