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


At 01:24 PM 7/7/2004, Rolf Campbell wrote:
Brian Dessent wrote:
mathiasdotwagneratphilipsdotcom 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

Sorry Rolf, but at least on my HT processor running Windows XP pro, the reporting of utilization by task manager is exactly as described by Brian.



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