Re: Hyperthreading - Oracle license
- From: Kevin Closson <ora_kclosson@xxxxxxxxx>
- To: "rjoralist2@xxxxxxxxxxxxxxxxxxxxx" <rjoralist2@xxxxxxxxxxxxxxxxxxxxx>, "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 11 Jan 2013 09:39:24 -0800 (PST)
SMT cores should be thought of as another .3 of a core...and platform experts
would do well to accept the new reality: 70 is the new 100
SMT is not a bad thing..not understanding it can be.
If I can get my head out of the foxhole without seeing tracers I actually have
a blog post teed up on SMT
The feature is called Simultaneous MultiThreading but since a thread is stalled
until its peer thread stalls (all the while the OS charges each of them against
their time slice over any given wall-clock period) I sort of poo-poo the use of
the word simultaneous.
No war-horse here, but best to test.
________________________________
From: Rich Jesse <rjoralist2@xxxxxxxxxxxxxxxxxxxxx>
To: oracle-l@xxxxxxxxxxxxx
Sent: Thursday, January 10, 2013 2:30 PM
Subject: RE: Hyperthreading - Oracle license
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.
I understand that the CPU_COUNT isn't based on the raw CPU power. Perhaps
the suggestion was made *assuming* the reader would somehow magically
consider recollecting system stats after turning on HT?
Call me paranoid (no, really, go ahead), but it just doesn't smell right...
Rich
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