Re: hyperthreaded cpu still an issue in 8.4?

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.

I think the Intel numbers says that Intel HT provides +15% performance
on average.

Cheers,
mark

--
Mark Mielke<mark(at)mielke(dot)cc>