ITEM: S2034L

Performance hits for using maxdata upon linking?

Question:

DESC:

An application we are building allows users to select modules
to include in an ad hoc program and then links the pieces
together and runs that program.  A small percentage of these
ad hoc programs will need more that one segment for data to
run.

Question:  What sort of performance hit will we take on ad hoc
programs which need only one segment but are linked with
maxdata set to more than one segment?  (That is, they will
never reference the second or subsequent segments.)

Question:  For that matter, what performance hit will we take
for programs which do use multiple data segments?
Question:  What sort of swap space and memory are necessary
for these larger programs?  (That is, we obviously need swap
or something for the data space as we call malloc, but what
about at load time?)

Response:

Assuming the system RAM is at least 256MB and is dedicated to your
"adhoc" application: If you set PSALLOC=late you won't take up
pagespace until you actually touch those pages in memory. This should
prevent paging on those programs using only 1 datasegment or less (ie. No
performance hit). For those programs touching more than one 256MB
segment, you'll get a page fault when you touch that region of memory
(not at load time). In this case if the most virtual memory needed is
3 segments + 1 for normal system activity then you would use at least 
1GB of Pagespace for this hypothetical system.

Please notice that use of -bmaxdata: option is not related to performance 
in either case.  



Support Line: Performance hits for using maxdata upon linking? ITEM: S2034L

Dated: July 1995 Category: N/A

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