Re: Auto Tuning

Mark,

There has always been an internal timeslice - this is the ~trick~ that
allows the box to appear as though it is multi-tasking. Certainly, this
internal timeslice has reduced drastically with new hardware, and of course,
with multiple processors there must be multiple internal timeslices.

However, the internal timeslice has never been a parameter that could be
used for tuning. It was never able to be changed, and still cannot be
changed. And, it has nothing to do with the external timeslice which is a
parameter for each job. And, the external timeslice is not used to assign an
actual machine timeslice at the level of the MI task.

I would be surprised if the algorithm has changed to ignore the external
timeslice. I would not be surprised if this is another piece of
misinterpreted information passed on as fact - that seems to be how most
tuning stories go... Still, if you can find a source for this, I would
welcome the education.

Trevor

----- Original Message ----- 
From: "Mark S. Waterbury"
Subject: Re: Auto Tuning


> Hello, all:
>
> With all the talk of "tuning" OS/400, I seem to recall, back when IBM
first
> introduced the RISC-based AS/400s, there were major internal changes
> "under the hood" due to the fact that the RISC PowerPC processors were
> so much faster than the IMPI CISC processors.
>
> I seem to recall that someone (perhaps an IBMer) told me that those
> values specified for the "timeslice" no longer directly affect the
internal
> timeslice used by the RISC processors. The machines are so much faster,
> and the PowerPC processes so many more instructions per second, that
> IBM decided to "ignore" that parameter, or only uses it as a "guideline"
> of some sort... internally they use a much, much smaller timeslice...
>
> Especially now that OS/400 supports threads and multi-threading within
> a single job/process.
>
> In other words, the external job level values you specify for timeslice
etc.
> no longer directly influence how SLIC assigns the actual machine "time
> slice" at the level of the MI task.
>
> (I am not sure what those system values really do any more.)
>
> Hope that helps...
>
> Mark S. Waterbury