Re: [Xen-users] xen build and tls

[John Haxby <john.haxby@xxxxxxxxxx>]

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.
jch



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