Discussion:
What does "Performance implications" signify?
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Charles Mills
2017-10-06 15:06:28 UTC
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Just a Friday curiosity question, triggered by Peter's response to my
question about doubleword alignment for an IEAVPSE parameter.

In the MVS macro write-ups, what does "Performance implications" signify? In
my limited experience, I don't recall ever seeing a value other than "None,"
even for things like ENQ SYSTEMS where there are definite performance
considerations. Is there an example where it is not "None"? What exactly is
"None" supposed to mean?

Charles

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Peter Relson
2017-10-07 12:59:50 UTC
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It signifies what you expect it to signify, but not down to the level of
micro-managing. I would view the difference between doubleword alignment
and not-so-aligned to be micro-managing,
Post by Charles Mills
I don't recall ever seeing a value other than "None,"
There are some (maybe even many). GQSCAN, for example.

Primarily I would think it might apply to operational differences between
choices when it seems important to let the user know.

Peter Relson
z/OS Core Technology Design


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scott Ford
2017-10-07 14:08:46 UTC
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Peter,

Loved the answer.. Would you agree how the macros is used and purpose being
factors in performance, speaking very
Generically..


Scott
Post by Peter Relson
It signifies what you expect it to signify, but not down to the level of
micro-managing. I would view the difference between doubleword alignment
and not-so-aligned to be micro-managing,
Post by Charles Mills
I don't recall ever seeing a value other than "None,"
There are some (maybe even many). GQSCAN, for example.
Primarily I would think it might apply to operational differences between
choices when it seems important to let the user know.
Peter Relson
z/OS Core Technology Design
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Scott Ford
IDMWORKS
z/OS Development

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Hobart Spitz
2017-10-08 14:33:18 UTC
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IIRC, the S/370s were somewhat affected by non-aligned doublewords, and the
impact has decreased with newer hardware, possibly to zero or nearly so.
If I had to guess, micro code advances, faster multi-level cache, and/or
out of order execution, have made any impact negligible.
Post by scott Ford
Peter,
Loved the answer.. Would you agree how the macros is used and purpose being
factors in performance, speaking very
Generically..
Scott
Post by Peter Relson
It signifies what you expect it to signify, but not down to the level of
micro-managing. I would view the difference between doubleword alignment
and not-so-aligned to be micro-managing,
Post by Charles Mills
I don't recall ever seeing a value other than "None,"
There are some (maybe even many). GQSCAN, for example.
Primarily I would think it might apply to operational differences between
choices when it seems important to let the user know.
Peter Relson
z/OS Core Technology Design
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Scott Ford
IDMWORKS
z/OS Development
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