two instances of a.exe on dual processor - still only 50% performance

[Rolf Campbell]

Brian Dessent wrote:
> mathias.wagner@philips.com wrote:
>>Many thanks for this tip. I tried it out and indeed there is a "Set
>>Affinity" option in the Taskmanager. Apparently, this option lets you
>>assign one or more of the 4 virtual processors to a particular task. (W2K
>>seems to have this concept of virtual processors, I am no expert at all
>>here). But it doesn't change a thing. still 50% are spent on Idle mode...
> You see 4 CPUs because of HyperThreading.  A HT CPU registers with the
> OS as two CPUs, but it's not.  Only in certain circumstances can it run
> two threads concurrently (such as performing an integer and floating
> operation at the same time.)  Thus 50% CPU usage means that your system
> is fully loaded.  On a HT system you've got to double all the CPU usage
> percentages for it to make sense.  Occasionally you might see it surpass
> 50%, which would mean that the hyperthreading is particularly suited to
> whatever combination of instructions is being executed and it's using
> the CPU more efficiently.
> 
> Brian
Sorry Brian, that is bogus.  I'm running one HT processor right now. 
The combined CPU utilization is not an actual display of usage, but 
theoretical usage, based on scheduling.  It's really how much of the CPU 
was NOT being used by the idle task, and given that there is only one 
CPU, if some process is taking up 99% of it, and some other process 
takse up the other 1% on the other 'hyper thread' then the idle task 
will not be able to run at all on either virtual cpu.  Thus Task Manager 
will (and does) show 100% dual CPU utilization.

Now, Mathias's problem:  Sounds like your program is bound by something 
other than CPU.  If you have two programs that try to access the 
hard-disk, they are not going to be twice as fast with 2 CPUs (virtual 
or not).

-Rolf


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