channel access

[john sinclair <sinclair@mail.phy.ornl.gov>]

In the course of testing edm, I have noticed the following behavior for
some configurations (unfortunately, I don't mean anything precise when I
say "some configurations"):

  I run a fresh copy of edm, bring up a display containing ~9000
  references to the same pv  and execute it. This adds ~9000 events to the
  ioc (or portable CAS). Performance is good.

  I now deactivate the display which clears all the events.

  From this point on, when this or any other display is executed, the
  performance is such that it takes twice as long to complete the
  process of adding all the events.



At this point the code looked something like the following:

====================================

  for all pvs {

    add events

  }

  ca_pend_io( time )

====================================



So, I changed this to

====================================

  count=0
  for all pvs {

    add events
    if ( ++count > someNumber ) {
      ca_pend_io( time )
      count=0
    }

  }

  ca_pend_io( time ) 

====================================



This did not help at all. Then I change to code to

====================================

  count=0
  for all pvs {

    add events           
    if ( ++count > someNumber ) {
      ca_pend_io( time )
      ca_pend_event( small-time )
      count=0
    }
 
  }

  ca_pend_io( time )
  ca_pend_event( small-time )

====================================



This made an amazing difference and now the performance is good all the
time.

Is this behavior reasonable? Does pend event do something fundamentally
different from pend io?


John Sinclair
sinclair@mail.phy.ornl.gov
Oak Ridge National Lab
865-576-6362   865-574-1268 (fax)