Mail Archives: cygwin/2004/07/07/13:34:29
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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