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@xxxxxxxxxx> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. + -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
