What about IBM's zPCR Windows program? That uses a base performance
number from an old z9EC as a reference, coming up with numbers which
look like single processor speeds that can be compared. For example:
http://www.mildredbrennan.com/mvs/zpcr.png
On 12/14/2019 7:28 AM, Charles Mills wrote:
Responding to @Phil, yeah, don't you love it: apply a magical fudge factor and then
report the results to five digits of precision. The good news is that both of the
machines in question are the same generation: they are both "z11's" so to speak
(z196 and z114).
Responding to @Scott, thanks, the most thorough explanation so far. Fortunately this is not "whether an
upgrade delivered the expected results?" or "which would be better, a used z14EC or a new
z15BC?" It is just "how do I compare the CPU times of two jobs on two different machines?"
Seems like a simple question, no?
The numbers below (from IBM.com) do not seem to support what you are saying however: "if you're trying
to convert CPU time between machines, the ratio of any of SUs, MSUs, or PCI will be pretty much equally
"fine"." The ratio of the PCI's of the two machines is about eight-to-one but they seem in
practice to be *about* the same speed: that is, a job that uses about 1 CPU second on one seems to use about
1 CPU second on the other (certainly not eight times as much!). The SU/SEC ratio for the two machines is
40404/33333 which seems to more accurately reflect observed reality (although way less than perfectly! --
less perfectly than a guess of "oh, I guess they are about the same speed").
Processor #CP PCI MSU MSUps Low Average High
2817-730 30 23,929 2,855 2,370 49.54 42.75 37.96
Processor #CP PCI MSU Low Average High
2818-Z05 5 3,139 388 6.18 5.61
4.77
In short, I'm still struggling for an answer to my simple <g> question: how do
I compare CPU times on two different machines?
Charles
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf
Of Scott Chapman
Sent: Saturday, December 14, 2019 4:48 AM
To: [email protected]
Subject: Re: How do I compare CPU times on two machines?
SUs, MSU, PCI (IBM MIPS) ratings are all just different magnitudes of the same
number. What I mean is that they all are calculated from the same LSPR tests
and exist in relatively fixed ratios to each other. There may be some slight
variations because (for example) MSUs and PCIs are quoted in whole numbers and
IBM seems to tweak them very slightly. The ratios differ slightly between
single and dual frame, full speed and sub-cap engines, and number of engines.
But for all practical purposes, the ratios hold within a couple percent.
Re. the "technology dividend" where they derated the MSUs relative to the SUs
(before they decided to deliver software price improvements by software price changes),
that only changed the ratios between MSUs and the SUs.
In the old days (before the "technology dividend") MSUs ~ SUs * CPUs * 3600
Now, for the last several generations of machines: MSUs ~ SUs * CPUs * 3600 *
0.664
With the z15, the ratio between SUs and PCI are even flatter than they were in prior generation.
I.E. my understanding is that they're doing much more of a straight-up calculation and not
"tweaking" (my term) the results as much as they did prior. (And to be clear: the prior
variation due to "tweaking" was not very much, it's just less with the z15.)
So in short, if you're trying to convert CPU time between machines, the ratio of any of
SUs, MSUs, or PCI will be pretty much equally "fine". Not necessarily accurate,
but all of them will be about the same.
If you want to be more accurate about it (such as evaluating whether an upgrade
delivered the expected results), then build zPCR models of the two machines in
question and use the ratios that it produces. But in all cases, the expectation
is that the ratio between the two machines is an average of many different
types of work. Individual work units will over- or under-perform expectations.
The hope (and real expectation) is that across all the work on the system you
come close (+/- 5%) to the ratio provided by zPCR. Reality may differ more
significantly from expectation if you're just using one of the single-number
metrics without regard to the RNI of the work and the LPAR configuration
(factors that zPCR takes into account).
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