Re: (disk/cpu) kernel performance problem
Mark Lord (mlord@pobox.com)
Tue, 27 Jul 1999 10:32:55 -0400
Gerald Aigner wrote:
..
> > Percentage of CPU time is not a useful measurement.
> > Think about it.. if I/O were infinitely fast, then CPU usage
> > would be 100%, since the CPU would never have to wait.
> >
> > If disk I/O were infinitely slow, CPU usage would be 0%,
> > but that's not a Good Thing, is it..
> >
> 45% is the amount of time the kernel spends in loading data from disk.
>
> The lower this value the more time is available for other
> threads/applications on the same system therefore increasing overall
> system utilization.
Okay, So install a *slower* disk, and you'll see that
number drop dramatically, to perhaps 15-20%. That is because
the overall elapsed time will increase, "reducing" the percentage
of CPU spent doing I/O, even though the total CPU utilization for
I/O remains unchanged (and quite small). Get it now?
--
mlord@pobox.com
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