Re: How are CPU Speed and Overall CPW Related?

["Alexei Pytel" <pytel@xxxxxxxxxx>]

Mhz and CPW are always a source of confusion - this is why IBM used to be
reluctant to publish Mhz ratings.
Mhz only measures CPU speed. But this is only one factor in overall system
performance. Other factors - of equal or even higher importance - cache
size, cache management algorithms use, memory size, memory bus speed,
memory chip speed, I/O bus speed, number of I/O buses, disk drive speed,
speed of internal bus between disk and disk controller card etc etc. And
not to forget software - efficiency of device drivers, system dispatching
and scheduling algorithms, code path length in various components etc etc.
All these are in a complicated interplay.

CPW is an attempt of a more integral measure of system performance. CPW is
measured on a commercial mix which is more or less similar to TPC-C. CPW
measures system throughput while processing this mix.

If system has faster CPU but smaller CPW it most probably means that it has
some kind of bottleneck - basically CPW mix cannot fully load CPU. Either
I/O is constrained - e.g. too few I/O buses -  or memory is constrained.

In short if your application is number-crunching type with few I/Os - Mhz
is good measure for you.
If you have to go to database for data - CPW gives a better estimate.

    Alexei Pytel

Note 1: governor has nothing to do with it
Note 2: because CPW takes software into account, it is not unusual that
different versions of OS will show different CPW for the same model.



                                                                                
                   
                    "Nathan M. Andelin"                                         
                   
                    <nathanma@haaga.com       To:     <MIDRANGE-L@midrange.com> 
                   
                    >                         cc:                               
                   
                    Sent by:                  Subject:     How are CPU Speed 
and Overall CPW       
                    owner-midrange-l@mi        Related?                         
                   
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                    04/30/2001 09:26 AM                                         
                   
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I had previously assumed that CPU speed and CPW rating were closely
related.
Apparently I was mistaken.  Midrange Computing recently published charts
that would suggest otherwise.  For example, the model 170-2160 has a 100
Mhz
Apache processor and a CPW rating of 114, while the model 170-2290 has a
200
Mhz Northstar processor and a CPW rating of only 73.  Can anyone explain
this?  Is there a governor on the 170-2290 that causes it to handle less
work than the 170-2160?

Thanks,

Nathan.


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