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Experimental Physics and
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<== Date ==> <== Thread ==>

Subject: [none given]
From: Sue Witherspoon <withers@cebaf.gov>
Date: Fri, 14 Apr 1995 11:01:17 -0400
Greetings,
  I am having trouble with execution speed after changing the scan 
period.
I have a lockset that utilizes the following scheme to change the scan
period. 
   ______________________________ 
  |  ________     ____________   | 
  | |(magRec)|   |(stringout) |  |
  | |--------|   |------------|  |
  | | HSCN   |-->|DOL  | OUT  |->|  
  | |--------|   |____________| 
  ->| SCAN   |
    |________| 

'magRec' is a custom record akin to a subroutine record. magRec.HSCN is
a string field set by the user to dynamically control the scan rate.

Initially, the magRec.SCAN and magRec.HSCN are PASSIVE.  When 
magRec.HSCN is set to ".1 second" the magRec.SCAN will change to 
'.1 second'. This all appears to work well, at least for one instance. 
There are many of these locksets on one ioc. When more than on lockset
are switched to '.1 second' the following results were:

1  is  switched   the record processes approximately 10 times a second
2  are switched   the record processes approximately 7 times a second 
3  are switched   the record processes approximately 4 times a second
42 are switched   the record processes approximately 1 time in 4 seconds

Additionally, I eliminated the stringout and set the magRec.SCAN to
".1 second".  Forty-two (42) records processed at 10 times a second, as
expected. 

The ioc remains more that 40% idle during all tests and the scanPeriods
never seemed to significantly use more CPU. My tools are:
 MVME-167  8Mb memory
 EPICS 3.11.0
 VxWorks 5.1.1

Why does the performance degrade when I change the SCAN field dynamically?
Thanks in advance.
_______________________________________________________________________
Sue Witherspoon
CEBAF
withers@cebaf.gov
(804)249-7579

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