Experimental Physics and
Industrial Control System

Ned Arnold <[email protected]> · Mon, 29 Mar 1999 08:14:32 -0600 (CST)

> Under circumstances which we have been unable to pin down we see the
> task called "EV recDynINP" take a substantial amount of the cpu on an
> IOC (this is with 3.12.2) - 20% on at least one occasion. Disconnecting
> all CA clients sometimes, but not always, sends it back to zero. Has
> anyone else seen this sort of effect ? What does "EV recDynINP" do ?
> From looking at the EPICS source code it appears to be used by the WAIT
> and SCAN records - our database has several wait records but no scan
> records.
> 

"EV recDynINP" is a task that is spawned to be the "CA client" for input links
of the wait and scan record. This allows the input links to be dynamically
changed without rebooting the ioc (a capability that ALL links have in R3.13).

This task looks for "monitors" to be posted on the input links. If these 
are being received frequently, the "EV recDynINP" will consume CPU resources.
With the wait record, it IS possible to build a loop in your database that
can consume all remaining CPU resources (if a wait record processes on an 
input change which results in an output that causes the input to change
immediately again).

Recommendations :

 > Use another CA client (cau or probe) to determine if the wait record input
   links are rapidly changing. See if database logic is "looping" 
   unnecessarily.

 > Determine how frequently the wait records are processing (setting .TPRO)
   will accomplish this.

 > Move to R3.13 and use the calcout record instead of the wait record (which
   has proven to be more robust and offers even more features)

 > See if the situation is dependent on whether the wait record input links
   are on the same ioc or connected via channel access. If the weird behavior
   is only on CA links, use an intermediate record (ai, calc) to fetch this
   data.

   Hope this helps. Send more details if none of the above is useful ... 

   	Ned

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System