How do I fix the 4gb seg fixup messages in my syslog?
These messages are from a glibc that was built with negative GS register offsets. Xen can run with negative GS register references, but it must “trap and emulate” this condition, which is relatively resource intensive, and quite slow. If you don’t have a patched glibc, see the no-tls-direct-seg-refs patch mentioned in XenSpecificGlibc. Most newer distributions are shipped with a “-mno-tls-direct-seg-refs” compiled glibc, but it might not be enabled by default. Some newer distributions like the RHEL5 Beta1/Beta2 require the ld.so.conf.d trick below to refer to the patched glibc. Some slightly older distributions like Ubuntu Dapper can be fixed with a simple rebuild of glibc: (see UbuntuDapperHowTo).
