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Re: [Xen-users] xen build and tls

To: Paras pradhan <pradhanparas@xxxxxxxxx>
Subject: Re: [Xen-users] xen build and tls
From: John Haxby <john.haxby@xxxxxxxxxx>
Date: Wed, 26 Nov 2008 10:31:05 +0000
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Paras pradhan wrote:
I have compiled (with initrd) xen 3.3 from source tar ball following the README file under centos 5.2. xen kernel boots fine but my system (2 cores, 2.0 GHZ, 1GB RAM) is slow with a warning message.

  ** WARNING: Currently emulating unsupported memory accesses  **
  **          in /lib/tls glibc libraries. The emulation is    **
  **          slow. To ensure full performance you should      **
  **          install a 'xen-friendly' (nosegneg) version of   **
  **          the library, or disable tls support by executing **
  **          the following as root:                           **
  **          mv /lib/tls /lib/tls.disabled                    **
  ** Offending process: modprobe (pid=849)                     **

Is my system slow due to this tls warning? or I can ignore the warning.

As it says in http://lists.xensource.com/archives/html/xen-users/2006-04/msg00594.html (and corrected slightly in the reply) you need to create a file called /etc/ld.so.conf.d/nosegneg.conf that contains something like this:

# This directive teaches ldconfig to search in nosegneg subdirectories
# and cache the DSOs there with extra bit 0 set in their hwcap match
# fields.  In Xen guest kernels, the vDSO tells the dynamic linker to
# search in nosegneg subdirectories and to match this extra hwcap bit
# in the ld.so.cache file.
hwcap 0 nosegneg

The file must have a ".conf" suffix and the critical line is that last one -- the rest is commentary. I copied it wholesale from, I think, a Fedora 8 machine where I had installed the xen rpms.

You don't need to install any special libc and ignore comments from people about renaming /lib/tls to /lib/tls.disabled. The former is because the CentOS (aka RHEL and also Fedora) glibc already has the necessary changes, the latter because it's an empty directory and renaming it to stop the runtime linker finding stuff doesn't help :-)

Also ignore people telling you that modprobe and init are statically linked on CentOS, they're not.

But for anyone else reading this in the archives -- remember that all of the above is CentOS/RHEL/Fedora specific: different distros do things differently.


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