Re: [Xen-users] Is NPTL in PV Xen Possible in RHEL5/CentOS 5 Distros?

[Nico Kadel-Garcia <nkadel@xxxxxxxxx>]

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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