Thank you all for comments. Joel, this is exactly what happens: if our rolling 4-hour MSU average starts with too high numbers in the morning, we are in trouble at noon. Of course that we monitor it and manage it, and constantly working on prevention (Werner, thank you for the idea of assigning classes dynamically using REXX - we'll see if it's suitable for us) . Still, sometimes capping happens. Then we have what Adam said, the situation that everything is either at the same priority or importance levels, competing for CPU cycles. During the same period of time that high DP workload is stalling and experiencing performance degradation, batch jobs with lowest dispatching priority manage to 'steal' certain amount of CPU. Therefore question if not allowing those jobs to execute would ensure that those CPU cycles are spent on high DP workload. Natasa
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