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 am also > unclear exactly what you tested, as I didn't see it mentioned in the > email --- CPU type, CPU count, and operating system would be the minimal > information required. Ooops! I thought I'd posted that earlier, but I didn't. The processors in question is the Intel(R) Xeon(R) CPU E7- 4850, with 4 of them for a total of 40 cores or 80 HT cores. OS is RHEL with 2.6.32-431.3.1.el6.x86_64. I've emailed a kernel hacker who works at Intel for comment; for one thing, I'm wondering if the older kernel version is a problem for a system like this. -- Josh Berkus PostgreSQL Experts Inc. http://pgexperts.com -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
