Stack-group switching time?

["Nakul P. Saraiya" <SARAIYA%sumex-aim.arpa@CSNET-RELAY>]

I need some way of getting a good cheap estimate of the time involved
in making a stack-group switch on a 36xx.  Or, more specifically, a
function that will take a sg as its argument and return an estimate of
the microseconds required to make it current.  The goal is to (more)
accurately time a `user' program through possible multiple scheduling
breaks.  Any leads/advice/data that will save me from empirically
trying to determine this function will be much appreciated.

				Nakul Saraiya
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