Okay. I got a Xen VPS host, because I can therefore install
whatever the hell I want and e.g. recode my vanity website in lisp.
So, installed SBCL in it, just playing about.
NPTL TLS, as implemented by GLIBC by default, works under xen but
has severe performance problems due to the implementation
technique. So... recompile glibc with -mno-tls-direct-seg-refs , as
indicated in http://wiki.xensource.com/xenwiki/XenSpecificGlibc
*** All well and good, but just in case: might sbcl
itself be generating native code that use segment offsets
in a Xen-unfriendly manner? It might not be at all, but I'm not
well-versed enough in sbcl internals to know, or even know
where to look.