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Re: Measurement of CPU usage
de Al Klein 05/08/2006 12:08
On 7 May 2006 07:41:59 -0700, "PaulFXH" <paul_hackett2@yahoo.com.br>
wrote:
>However, looking at the FreeMeter homepage, it describes what it calls
>"CPU Usage" as the "percentage of time that the CPU is busy".
>You commented earlier that CPU usage should always be close to 100%.
Nope - the CPU is ALWAYS executing *some* instruction (unless it
executed a HALT instruction, in which case it's stopped), so usage is
always 100%. Not 99,9%, not 100.1% - always exactly 100%. Which is
why measuring total CPU usage doesn't tell you anything.
>If we assume that in fact it's not normally that close in reality and
>that the 60-80% numbers churned out by FreeMeter, (among others) are
>truly what they claim, i.e. the percentage of time that the CPU is busy
>(including doing System Idle Processes).
As I said, that's impossible - the CPU is ALWAYS executing an
instruction.
>Then, on the other hand, if we suppose that Process Explorer (and
>WinTop and Task Manager) distributes the % of the CPU use to the
>various processes currently running but ONLY FOR THE TIMES THE CPU IS
>BUSY, then we would have an explanation.
That would be nice, but it won't work.
>For this reason, the total of all the CPU time being used by the
>various running processes in Process Explorer is always close to
>100%---because it only makes the calculation WHEN THE CPU IS BUSY.
No, since the CPU, if you define "busy" as "executing instructions",
is always busy. At least until you turn the computer off.
If the program is giving you a measure of
"cpu-in-use-but-not-executing-System Idle Process", it may be
accurate. But if it's claiming that the CPU is only being used 60-80%
of the time, it's lying. If the CPU is doing "nothing", it's
executing a wait loop (called System Idle Process), waiting for
something to happen.