Xen users - Aug 2007 - Is NPTL in PV Xen Possible in RHEL5/CentOS 5 Distros?

I''m in a bit of a bind.  My organization is planning to move to a new 
mail system and I really want this box to be up as close to 24x7 as 
possible.  I am currently working on an HVM domain running RHEL on top 
of CentOS.  What I''m concerned about is the issue of I/O (disk and 
network) since a mail system will be very busy in that way.  The mail 
app I''m planning on running needs NPTL.  When I tried a paravirtualized
Fedora Core a few years back, the installer for that app said it 
wouldn''t install since the kernel didn''t have NPTL.  So this
led me to
believe that I had to wait for HVM.  Now, I''m not so sure...  In my 
recent searches, I''ve seen that all that''s really required is
a glibc
that supports NPTL and that if one runs Xen this way, you wind up with 
slow performance.  I suspect this has something to do with the TLS lib 
that many Xen docs say to rename?

So has anyone made a glibc that will install on RHEL or CentOS that is 
Xen friendly at this point?  If so, I may be in much better shape than I 
thought.

Thanks.


-- 
George Lenzer
Computer and Networking Specialist
Cleveland Public Library
Automation Department


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> I''m in a bit of a bind.  My organization is planning to move to a
new
> mail system and I really want this box to be up as close to 24x7 as
> possible.  I am currently working on an HVM domain running RHEL on top
> of CentOS.  What I''m concerned about is the issue of I/O (disk and
> network) since a mail system will be very busy in that way.  The mail
> app I''m planning on running needs NPTL.  When I tried a
paravirtualized
> Fedora Core a few years back, the installer for that app said it
> wouldn''t install since the kernel didn''t have NPTL.  So
this led me to
> believe that I had to wait for HVM.
You''re right that HVM ought to work for you.
> Now, I''m not so sure...  In my 
> recent searches, I''ve seen that all that''s really
required is a glibc
> that supports NPTL and that if one runs Xen this way, you wind up with
> slow performance.  I suspect this has something to do with the TLS lib
> that many Xen docs say to rename?
In the olden days, if you didn''t rename the TLS lib (to disable it)
then Xen
would have to do a whole load of emulation.  Ought to be correct, but would 
cause some slowdown.

RHEL5 and CentOS 5 ship a glibc setup which is Xen aware and will do the Right 
Thing when used on a Xenified kernel.  It should Just Work for you.
>
> So has anyone made a glibc that will install on RHEL or CentOS that is
> Xen friendly at this point?  If so, I may be in much better shape than I
> thought.
RHEL and CentOS ship with Xen.  The glibc they ship ought to work (at least, 
it ought to work with their kernels, and I assume it''ll work with
others)
with good performance and without you having to make any manual configuration 
changes.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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Mark Williamson wrote:
>> I''m in a bit of a bind.  My organization is planning to move
to a new
>> mail system and I really want this box to be up as close to 24x7 as
>> possible.  I am currently working on an HVM domain running RHEL on top
>> of CentOS.  What I''m concerned about is the issue of I/O (disk
and
>> network) since a mail system will be very busy in that way.  The mail
>> app I''m planning on running needs NPTL.  When I tried a
paravirtualized
>> Fedora Core a few years back, the installer for that app said it
>> wouldn''t install since the kernel didn''t have NPTL. 
So this led me to
>> believe that I had to wait for HVM.
>>     
>
> You''re right that HVM ought to work for you.
>
>   
>> Now, I''m not so sure...  In my 
>> recent searches, I''ve seen that all that''s really
required is a glibc
>> that supports NPTL and that if one runs Xen this way, you wind up with
>> slow performance.  I suspect this has something to do with the TLS lib
>> that many Xen docs say to rename?
>>     
>
> In the olden days, if you didn''t rename the TLS lib (to disable
it) then Xen
> would have to do a whole load of emulation.  Ought to be correct, but would
> cause some slowdown.
>
> RHEL5 and CentOS 5 ship a glibc setup which is Xen aware and will do the
Right
> Thing when used on a Xenified kernel.  It should Just Work for you.
>   
Amusingly, it''s actually not the kernel or glibc itself. They kernel
RPM
installs a configuration file in /etc/ld.so.conf.d that blocks access to 
the /lib/tls libraries. I haven''t tried performance testing with this, 
but I''d be very interested to see results of trying this stunt with a 
Xen published or locally configured Xen kernel.

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