Superdome2 and hyperthreading enabled at the hardware level.

[TwoProc]

So, I've got a question re: Superdome2 running HPUX 11.3 (Tukwilla).

I've been told that having hyperthreading turned on at the hardware level, but not at the OS level will affect performance, in that the even though the OS doesn't recognize it, the hardware layer underneath is still trying to implement and use the extra "chips" if you will. I've been told this does adversely affect performance.

Does anyone have documents or a reference to this as being a fact, or not a fact?

And, in case you're wondering why I'd have it turned on at the hardware layer and not at the OS: When it's running as an OLTP system during the day, it runs much better with hyperthreading turned off at the OS layer (and this is common), but at night, when almost no users are on the system, batch processing of all kinds of things run better with hyperthreading turned on. Well, since it's a dynamic setting, we plan to use it that way.

So, if anyone has seen something showing that I'm hurting day time OLTP performance by having it turned off at the OS level, but still on at the hardware level, or documents that state the opposite, please let me know.

Much appreciated!

[Torsten.]

The only information I found regarding this is

"NOTE: Once hyperthreading is enabled for an nPartition, it is still necessary to configure that partition's operating system to use it. For HP-UX, this means changing the value of the kernel parameter lcpu_attr to 1."

So I think the main difference between SD2 and older systems is, it is now enabled by default, for previous systems it was disabled by default.