2009/7/21 Mark Mielke <mark@xxxxxxxxxxxxxx>: > On 07/21/2009 10:36 AM, Grzegorz Jaśkiewicz wrote: > > On Tue, Jul 21, 2009 at 3:16 PM, Scott Marlowe<scott.marlowe@xxxxxxxxx> > wrote: > > > On Tue, Jul 21, 2009 at 6:42 AM, Doug Hunley<doug@xxxxxxxxxxxxxxxxx> wrote: > > > Just wondering is the issue referenced in > http://archives.postgresql.org/pgsql-performance/2005-11/msg00415.php > is still present in 8.4 or if some tunable (or other) made the use of > hyperthreading a non-issue. We're looking to upgrade our servers soon > for performance reasons and am trying to determine if more cpus (no > HT) or less cpus (with HT) are the way to go. Thx > > > This isn't really an application tunable so much as a kernel level > tunable. PostgreSQL seems to have scaled pretty well a couple years > ago in the tweakers.net benchmark of the Sun T1 CPU with 4 threads per > core. However, at the time 4 AMD cores were spanking 8 Sun T1 cores > with 4 threads each. > > > Unless he is doing a lot of computations, on small sets of data. > > > Now I am confused, HT is not anywhere near what 'threads' are on sparcs > afaik. > > Fun relatively off-topic chat... :-) > > Intel "HT" provides the ability to execute two threads per CPU core at the > same time. > > Sun "CoolThreads" provide the same capability. They have just scaled it > further. Instead of Intel's Xeon Series 5500 with dual-processor, quad-core, > dual-thread configuration (= 16 active threads at a time), Sun T2+ has > dual-processor, eight-core, eight-thread configuration (= 128 active threads > at a time). > > Just, each Sun "CoolThread" thread is far less capable than an Intel "HT" > thread, so the comparison is really about the type of load. > > But, the real point is that "thread" (whether "CoolThread" or "HT" thread), > is not the same as core, which is not the same as processor. X 2 threads is > usually significantly less benefit than X 2 cores. X 2 cores is probably > less benefit than X 2 processors. Actually, given the faster inter-connect speed and communication, I'd think a single quad core CPU would be faster than the equivalent dual dual core cpu. > I think the Intel numbers says that Intel HT provides +15% performance on > average. It's very dependent on work load, that's for sure. I've some things that are 60 to 80% improved, others that go negative. But 15 to 40% is more typical. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
