Re: hyperthreaded cpu still an issue in 8.4?

2009/7/21 Mark Mielke <mark(at)mark(dot)mielke(dot)cc>:
> On 07/21/2009 10:36 AM, Grzegorz Jaśkiewicz wrote:
>
> On Tue, Jul 21, 2009 at 3:16 PM, Scott Marlowe<scott(dot)marlowe(at)gmail(dot)com>
> wrote:
>
>
> On Tue, Jul 21, 2009 at 6:42 AM, Doug Hunley<doug(at)hunley(dot)homeip(dot)net> 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.