Re: How are CPU Speed and Overall CPW Related? -- MIDRANGE-L

I'm devoted to OS/400.  I build OS/400 based applications for people.  My
current focus is Web development.  I'd like my applications to be able to
compete against their Windows counterparts.  But my customers are faced with
a dilemma.  I'll try to illustrate with an example:

 D theString       S             50A
 D theShorter      S             50A   Inz('TEST STRING')
 D nbr             S             10I 0
 D Secs            S             10I 0

 D Now             S               Z
 D Then            S               Z

 C                   Time                    Then

 C                   Do        100000        nbr
 C                   Eval      theString = %trim(theShorter)
 C                   EndDo

 C                   Time                    Now

C     Now           Subdur    Then          Secs:*MS

C     Secs          Dsply

C                   SetOn                                        LR
C                   Return

This simple program displays the number of milliseconds required TRIM blanks
from a 50 byte string and assign the result to another string variable -
100,000 times.

Let's take a look at an equivalent program, written in Visual Foxpro, and
running under Windows:

theString = space(50)
theShorter = 'TEST STRING'
theShorter = theShorter + space(50 - len(theShorter))

then = seconds()

for i = 1 to 100000
  theString = alltrim(theShorter)
endfor

now = seconds()

? now - then

It takes 2095 MS to run the RPG code on my AS/400.  But it only takes 365 MS
to run the Foxpro code on my Laptop.  The Foxpro program offers 5.74 times
better performance.  But Foxpro is not faster than RPG.  The difference is
in the computer hardware.

My Laptop CPU offers a 330 Mhz clockspeed.  My AS/400 offers a 200 Mhz
clockspeed.  That explains a small part of Foxpro's superior performance.  I
believe the more meaningful difference is that AS/400 CPU is not fully
utilized.

Alexei Pytel gave me a hint that jogged my memory.  Some time ago, I read
that CPU throughput was governed largely by cache - not only clockspeed.  My
theory is that Rochester governs CPU throughput via processor cache.

A Midrange Computing chart shows that the same 200 Mhz Northstar processor
offers a CPW range of between 50 and 220.  Actually a 100 Mhz Apache
processor offers a CPW of 210.  This indicates that a lowly 100 Mhz
processor is capable of running my CPU bound RPG program 3 times faster than
my 200 Mhz processor.

Is "64 bit RISC" meaningful?  Is "silicon on wafer" meaningful?  Not if you
put a governor on the CPU.  Or, should I say, not if you withhold processor
cache?

Bottom line.  Web applications do large amounts of string handling.  And
that requires large amounts of CPU time.  Why not unbridle the AS/400 CPU?
Otherwise, Joe Foxpro, VB, Delphi, and C Sharp programmer is going to kill
me.

Nathan.


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