Performance monitoring?

[bscott at ntisys.com]

On Fri, 20 Dec 2002, at 1:47pm, gnhlug at sophic.org wrote:
> Well, if he's using DMA, then technically none (or at least
> very little).

  Well, okay, yah.  When I said "waiting for the disk", I didn't mean "doing
nothing else", but rather "doing something else (including running the idle
loop) while waiting for the disk".  Upon further consideration, I suppose
interrupt latency (i.e., disk completes request, but system is busy doing
something else, so the ISR does not get called immediately) would affect my
suggested algorithm.  But you could probably make up a good excuse for
including interrupt latency in the benchmark.  ;-)

> It sounded to me he was trying to get an idea of how often requests
> weren't being serviced because the disks were already busy.

  He specifically said he was after "disk busy time", which I presume to
mean he wants to know what percent of time the disk drive is not idle.  
Rather like the "CPU utilization" (percent of CPU time not spent in the
kernel idle loop).

-- 
Ben Scott <bscott at ntisys.com>
| The opinions expressed in this message are those of the author and do not |
| necessarily represent the views or policy of any other person, entity or  |
| organization.  All information is provided without warranty of any kind.  |