Re: Turn off Hyperthreading! WAS: 60 core performance with 9.3

On Thu, Aug 21, 2014 at 02:02:26PM -0700, Josh Berkus wrote:
> On 08/20/2014 07:40 PM, Bruce Momjian wrote:
> > On Wed, Aug 20, 2014 at 12:13:50PM -0700, Josh Berkus wrote:
> >> On a read-write test, it's 10% faster with HT off as well.
> >>
> >> Further, from their production machine we've seen that having HT on
> >> causes the machine to slow down by 5X whenever you get more than 40
> >> cores (as in 100% of real cores or 50% of HT cores) worth of activity.
> >>
> >> So we're definitely back to "If you're using PostgreSQL, turn off
> >> Hyperthreading".
> >
> > Not sure how you can make such a blanket statement when so many people
> > have tested and shown the benefits of hyper-threading.
>
> 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.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + Everyone has their own god. +