In ancient times it was common practice to do this sort of thing...

SWITCH NOP GO
              MVI  SWITCH+1,X'F0'

I believe this clears the cache and causes severe performance hits

In my research into TESTCB for the z390 Project I found that it dynamically 
builds the subject instruction for an EX

Would this have the same performance hit ?

Melvyn Maltz.

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