[Info-vax] Raxco VMS Tuning Seminar Notes

[jls]

On Mon, 8 Nov 2010 14:03:36 -0800 (PST), Neil Rieck
<n.rieck at sympatico.ca> wrote:

>
>>
>> Right, the only reason to do more aggressive memory management /
>> reclamation is when you're in a memory starved environment.  However,
>> just out of curiosity, do you use AWSA on the DS20e?  According to the
>> RAXCO bible, it was encouraged for use in ALL (or nearly all)
>> circumstances.
>>
>
>First off, everyone uses AWSA-expansion so I think you are asking
>whether I use AWSA-reduction on my DS20e and the answer is no. Why?
>I've got 3 GB of RAM so it makes no sense not to use it. Also,
>swapping on a VAX was much more expensive than on Alpha and Itanium.

The rule-of-thumb makes no distinction.  It says ALWAYS set PFRATL
above zero.

>
>BTW, the "Raxco Bible" you are referring to describes rule-of-thumb
>rules for an older technology (VAX) from an older time.
>1) Swapping was more expensive on VAX than it is on Alpha.

Everything is more expensive on VAX than on Alpha, performance-wise.
However, swapping was much improved in VMS 4.x (iirc) and this old
rule-of-thumb no longer applied.

>2) VMS tuning parameters are still there but are used in a different
>way on modern systems. For example, VAX tuning emphasized a large
>FREELIST while big memory Alpha tuning (with large memory) emphasizes
>a smaller FREELIST. With a large FREELIST, a shrinking process would
>surrender pages to the FREELIST then soft-fault them back as needed.
>Getting the right balance between soft-fault (painless) and hard-fault
>(more painful) on VAX was preferable to swapping (dreadful).

Actually, even on VAX I learned that a larger modified vs freelist
helped speed things up, in some cases.  It could drastically reduce
the number of hard faults.

The places I worked for didn't spend their money on the system to keep
the memory free, they spent that money to get work done.  A larger
freelist tended to cause pages to get flushed from the modified list
sooner, which resulted in greater hard faulting.

VAX or Alpha, this didn't matter that much.