There's no reason you can't issue multiple EXCP's against the same DCB before issuing any WAIT's. IOS will queue the requests in the order they are received and if the requests are eligible for PAV processing, IOS will take care of it for you. Much ado about nothing here ?? Remember that even with PAV you're only allowed a single channel program to be active on any single extent. (Or at least that used to be true! <G>)
But it comes down to how I program my application in terms of having multiple outstanding EXCPs. Implicit in your comment is that it is natural to have multiple EXCPs outstanding at a time, so therefore there's nothing to do to exploit PAV. However the "simplest" approach to what I'm doing is to only have one outstanding EXCP, and when I get asked to write a block WAIT on the outstanding EXCP, then set off another one. That way the application logic is overlapped with the I/O. The question is, is it worth going any further. How many EXCPs is it worth having outstanding? Is two better? 20? There's no point in implementing code that will have multiple outstanding EXCPs, greatly increasing the complexity, if all that's going to happen is that they are going to be executed serially anyhow. Thus my attempt to understand EXCP queuing and PAV.
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