Re: [Xen-users] /lib/tls.disable vs. software requiring tls

[Ernst Bachmann <e.bachmann@xxxxxxxx>]

On Tuesday 14 March 2006 20:11, you wrote:
> Hi,
>
> but what about tomcat ? I use jre (java binary) which is linked to tls
> (thread local storage) :
>
> ldd /opt/jre/bin/java
>          linux-gate.so.1 =>  (0xffffe000)
>          libpthread.so.0 => /lib/tls/libpthread.so.0 (0xb7f34000)
>          libdl.so.2 => /lib/tls/libdl.so.2 (0xb7f30000)
>          libc.so.6 => /lib/tls/libc.so.6 (0xb7df9000)
>          /lib/ld-linux.so.2 (0xb7f4b000)
>
> when i start a tomcat instance in a xen domU, i get lot of processes
> instead a single (but multi-threaded) process ?
>
Thats because in the old thread library each thread got its own process ID, 
the kernel had only little support for threads, so it had to be done that 
way.
(With nptl, they still have an own PID, but its hidden from the userspace 
better)

Without xen, nptl provides a huge speed boost to threaded applications (esp 
Java), so you really should try to get a xen-compilant NPTL glibc running.
=> no speed loss from xen emulating TLS, but all the benefits from futexes, 
fast context switch between threads, ...

So, moving /lib/tls away is just a quick workarround, installing a "fixed" 
glibc is a solution.

/Ernst

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