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From: schwartz@gondor.psu.edu (Scott E. Schwartz)
Newsgroups: comp.arch,comp.os.misc
Subject: Re: Shared libraries (Was: Re: Big Programs Hurt Performance)
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Date: Tue, 29-Sep-87 12:28:43 EDT
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Posted: Tue Sep 29 12:28:43 1987
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Here is an antecdote that describes the ups and downs of runtime linking
of shared libraries (which is often how it is done).

In revision 20 of Primos Prime introduced dynamically linkable
shared libraries, which they call EPF's (for Executable Program Formats).
Previously, privliged software could be shared, but not user code.
Also, you had to dedicate a chunk of address space to the library.  In
rev 20 they made the whole system more general, and allowed user code
to be dynamically linked at runtime to a single copy of the library.
The increase in functionality was very large: it became easy to do lots
of things that had been hard in rev 19, and executables became very
small.  On the other hand, OS performace declinded dramatically.  A
prime 9950 that could comfortably support 80 users at rev 19 became
sluggish with 30 users at rev 20.  Now, there was probably a fair
amount of revision in the OS, so it's hard to claim that the new
style EPFs are the cause of the performance loss, but it is 
possible. 


#disclaimer  "Just my uninformed opinion."


-- Scott Schwartz            schwartz@gondor.psu.edu