Foreign Memory Problem

[utzoo!decvax!ucbvax!unix-wizards]

>From menlo70!hao!pag at Berkeley Sun Dec 27 07:39:25 1981
After lengthy performance analysis of our 11/70 UNIX, we determined
that the biggest bottleneck was swapping (avg 5-10 swaps/sec, as much as
25 swaps/sec during heavy use).  We had 512KB of core memory, and
decided to double it with an additional 512KB.  Due to cost considerations
we purchased a Plessy PM-SJ11 MOS memory system (which connects to
existing DEC MJ11 core memory).  So now our response is really
great, right?  WRONG!  There has been a noticeable slowdown in overall 
response time.  In fact, it is even slower in single user mode! (The file
system checks take longer).  Performance analysis indicates that the
only real difference is that swapping has decreased to near nil, other
factors (context switches, system calls, buffer hits, char and block i/o,
interrupts) remain the same.  In fact, the system is equally slow even if
the new memory is not being used.  So it has been bothering me to come up
with an explanation for this strange behavior.  Can anyone think of
an explanation (hardware, hopefully)?
    More details of complete memory system:
    128KB DEC MJ11B core in one chassis
    256KB Trendata/Standard Memories core (separate chassis)
    128KB DEC MJ11B core in 2nd chassis
    512KB Plessy PM-SJ11 MOS & terminators

The order of the list is also the cabling order (ie, Trendata memory lies
between two DEC boxes, and memory is terminated in Plessy box).  Soon
we will scope the system for memory cycle time, but haven't done that yet.
Any insight into this problem will be greatly appreciated.
					Thanks,
					peter gross
					ucbvax!menlo70!hao!pag
					CSVAX.pag at BERKELEY