Re: Hyperthreading - Oracle license
- From: Alex Fatkulin <afatkulin@xxxxxxxxx>
- To: rjoralist2@xxxxxxxxxxxxxxxxxxxxx
- Date: Fri, 11 Jan 2013 14:42:02 -0500
I don't read the tone of the note as "recommends", more like saying
that it's fine to have it 2x and "potentially providing greater
throughput and improved performance".
The goal of HT was to provide better throughput when exceeding
physical number of CPUs compared to the case where HT is turned off by
utilizing the fact that two threads can archive better pipeline
utilization by filling in "voids" left by the other thread. This is
why HT provides a lot of benefits on the "branchy" code where
execution pipeline is having a hard time keeping efficiency up.
Modern Intel CPUs (SandyBridge) got very sophisticated in how they
manage HT. Where previous generations required static partitioning of
some execution resources for each thread (which sometimes lead to a
lower per-thread performance with HT enabled) SB does a lot of
allocation dynamically depending on the thread workload.
On SUN (Oracle) SMT the cpu_count reported by the OS does lead to
other calculated parameters (parallel_max_servers, etc.) to be really
on a high side though.
On Thu, Jan 10, 2013 at 5:30 PM, Rich Jesse
<rjoralist2@xxxxxxxxxxxxxxxxxxxxx> wrote:
> Mark writes:
>
>> Actually, a quick MOS search, and Oracle specifically recommends staying w/
>> the "doubled" count for cpu_count.
>>
>> See Doc ID 289870.1
>
> I saw that, too, and I'm calling "BS" on the lack of evidence, empirical or
> otherwise. Unless it can be claimed that turning HT on gives one at or near
> a 100% gain in CPU power, it stands to reason that Oracle cannot consume at
> or near an additional 100%. And I'm reasonably certain that no one is
> advocating HT as giving anywhere near another the performance of another
> core.
>
--
Alex Fatkulin,
http://afatkulin.blogspot.com
Enkitec,
http://www.enkitec.com
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