On Thu, Aug 21, 2014 at 02:17:13PM -0700, Josh Berkus wrote:
> >> Actually, I don't know that anyone has posted the benefits of HT. Link?
> >> I want to compare results so that we can figure out what's different
> >> between my case and theirs. Also, it makes a big difference if there is
> >> an advantage to turning HT on for some workloads.
> >
> > I had Greg Smith test my system when it was installed, tested it, and
> > recommended hyper-threading. The system is Debian Squeeze
> > (2.6.32-5-amd64), CPUs are dual Xeon E5620, 8 cores, 16 virtual cores.
>
> Can you post some numerical results?
>
> I'm serious. It's obviously easier for our users if we can blanket
> recommend turning HT off; that's a LOT easier for them than "you might
> want to turn HT off if these conditions ...". So I want to establish
> that HT is a benefit sometimes if it is.
>
> I personally have never seen HT be a benefit. I've seen it be harmless
> (most of the time) but never beneficial.
I know that when hyperthreading was introduced that it was mostly a
negative, but then this was improved, and it might have gotten bad
again. I am afraid results are based on the type of CPU, so I am not
sure we can know a general answer.
I know I asked Greg Smith, and I assume he would know.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +