[CentOS-devel] Re: CentOS5 virtual machine image

Nils Toedtmann centos-mail at nils.toedtmann.net
Wed Jan 31 21:45:05 UTC 2007

Am Samstag, den 27.01.2007, 00:15 -0700 schrieb Bernard Johnson:
> Nils Toedtmann wrote:
> > I guess they did not disappear but got hidden. AFAIK (correct me if i am
> > wrong) recent xen versions have a hack to workaround TLS-libs silently,
> > but there is still a performance penalty. 
> That was not my understanding, however you may be right. Can you point
> me to documentation as to what the workaround actually does?  And what
> performance penalty we might be paying?

Am Sonntag, den 28.01.2007, 18:45 +0000 schrieb Karanbir Singh: 
> Do you have some numbers to elaborate on the point of performance loss ?

OK, i digged the MLs ...

If there are Xen-incompatible NPTL/TLS libs, then Xen3 does a "TLS
emulation" which gives threaded apps a performance penalty, at least on
i86_32 systems (i am not sure about i86_64):

  <http://wiki.xensource.com/xenwiki/XenFaq> (item 4.1)

This mail 


from Xen developer Keir Fraser is 9 days old and references to Xen 3.0.4
(which unfortunatly _needs_ TLS in Dom0 for xen-libs):

  "For now you can simply use the /lib/tls libraries — you’ll get a
   warning during boot and performance in domain0 will be reduced"

>From the rumors i have read on the xen MLs, OpenLDAP and java suffer
from that problem heavily, but i did not find benchmarks comparing
xen-compatible vs. xen-emulated TLS. Sorry, that is all i can tell on
that topic, i'm just another admin reading MLs...


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