Starting an OpenMP parallel section is extremely slow on a hyper-threaded Nehalem

[Tim Prince]

On 2/11/2010 2:00 AM, Edwin Bennink wrote:
> Dear gcc list,
>
>
> I noticed that starting an OpenMP parallel section takes a significant 
> amount of time on Nehalem cpu's with hyper-threading enabled.
>
If you think a question might be related to gcc, but don't know which 
forum to use, gcc-help is more appropriate.  As your question is whether 
there is a way to avoid anomalous behaviors when an old Ubuntu is run on 
a CPU released after that version of Ubuntu, an Ubuntu forum might be 
more appropriate.  A usual way is to shut off HyperThreading in the BIOS 
when running on a distro which has trouble with it.  I do find your 
observation interesting.
As far as I know, the oldest distro which works well on Core I7 is 
RHEL5.2 x86_64, which I run, with updated gcc and binutils, and HT 
disabled, as I never run applications which could benefit from HT.

-- 
Tim Prince