[Skimmertalk] CW Skimmer - more

[David Robbins K1TTT]

That could be extra windows overhead.  It is likely that the cpu time used
as sampled by the application can only report the actual time spent in it's
own process.  There are times however, especially if you are using the
computer for multi-tasking, when windows has to move things in and out of
memory.  This would be done outside of the actual program cpu usage so the
program built in meter may not register it, but the task manager would.  You
could probably provoke such behavior by using another program that uses lots
of memory.  The less memory the skimmer has to work with the more of this
swapping in and out of memory is needed.  Look up terms like 'page faults'
or 'context swapping' and how windows does multi-tasking and memory
management.


David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
 

> -----Original Message-----
> From: Pete Smith [mailto:n4zr at contesting.com]
> Sent: Tuesday, November 11, 2008 22:34
> To: skimmertalk at contesting.com; SDR-IQ at yahoogroups.com;
> dxatlas_group at yahoogroups.com
> Subject: [Skimmertalk] CW Skimmer - more
> 
> Now that I've proved (to myself at least) that I'm not completely nuts,
> let
> me prevail on your patience with a slightly more complicated question.
> 
> Under normal circumstances, I understand that CW Skimmer's own CPU usage
> indicator will normally show a somewhat higher number than Task Manager's,
> because it is looking at peaks from one application while Task Manager
> looks at an average over a second of so of all the processes that are
> going on.
> 
> That being said, I find that there is a pretty logical and explicable
> relationship among the Skimmer CPU number, the bandwidth set on the Radio
> tab, the number of decoders, and the number of candidate data streams (the
> last two are the "98 of 456 decoders" numbers).
> 
> Incidentally, it's little-known, but the Sample Rate choice on the Radio
> tab *does* affect both the bandwidth covered by an SDR-IQ when used with
> Skimmer and (therefore) the CPU demand.  To verify this, bring up Skimmer
> and change from 48 to 96 KHz.  You'll see the CPU loading go 'way up.
> 
> Finally, here's the question.  Have you ever noticed a situation in which
> the CPU utilization of the total of the two Skimmer processes) as reported
> by Task Manager is much higher than the CPU utilization being reported by
> Skimmer?  I see this all the time, but have not been able to figure out
> what causes it, or what makes it go away.  All I know for sure is that
> sometimes something is happening to impose a much higher load on the CPU
> for a given number of decoders than is the case at other times.  Sometimes
> I'll see this as much higher CPU utilization in 48 KHz mode than in 96 KHz
> mode.  Sometimes I can cause things to revert to normal by changing Sample
> rates, stopping and restarting the waterfall, or restarting the program.
> 
> One good question that Alex asked was whether it might be a mistake by the
> Task Manager.  All I can say is that I don't think so, because there is a
> definite slowing of other programs when Task Manager says utilization is
> over 85 percent, even though Skimmer itself says it is only using 50-55
> percent.  Moreover, I see the same phenomenon in Process Explorer, which
> is
> a completely separate program - I can't be sure that it doesn't measure
> CPU
> utilization the same way, of course, but it seems to be a stretch, because
> Process Explorer was not developed by Microsoft.
> 
> Anyway that's the question - if you could, just keep your eyes peeled, or
> run some tests, whatever you have time for.
> 
> Thanks and
> 
> 73, Pete N4ZR
> the World Contest Station Database is back...
> www.conteststations.com
> 
> 
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