[Xen-bugs] [Bug 788] mv /lib/tls confusion

[bugzilla-daemon@xxxxxxxxxxxxxxxxxxx]

http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=788





------- Comment #1 from samuel.thibault@xxxxxxxxxxxx  2007-11-27 05:51 -------
Both are.  What happens is that on x86, TLS uses direct negative offsets, which
can't be safely run natively, so that Xen has to emulate it, which is very
slow.  To sum it up:

1) TLS libc with direct negative offsets is very slow because Xen has to
emulate all libc TLS accesses.
2) non-TLS libc is a bit slow because libc then accesses TLS data `by hand'.
3) TLS libc with indirect negative offsets is less slow because it uses true
TLS mecanism, but without requiring Xen emulation.

Unfortunately, very few distributions provide 3) (debian does in the libc6-xen
package for instance), so that people end up with 1), which is very bad, thus
the common advice to mv tls tls.disabled, so as to get into 2).  However, that
advice doesn't work any more with glibc starting from 2.6, which _requires_
TLS, so that there's no 2) anymore, and people will have to ask their
distributions to provide 3).


-- 
Configure bugmail: 
http://bugzilla.xensource.com/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are the assignee for the bug, or are watching the assignee.

_______________________________________________
Xen-bugs mailing list
Xen-bugs@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-bugs