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From: "Serge A. Babkin" <babkin@hq.icb.chel.su>
Message-Id: <199605160309.JAA29241@hq.icb.chel.su>
Subject: EDO & Memory latency
To: hackers@freebsd.org
Date: Thu, 16 May 1996 09:09:12 +0600 (ESD)
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I have just tried lmbench and the numbers it gives are looking
slightly strange for me. It shows memory latency upto 500ns while
I have 60-ns EDO memory in a Pentium/75 box. Okay, its external
clock is 25MHz, this gives 40ns, one wait state, it gives another 40ns,
it gives 80ns, but why the overhead is over 400ns ? 

Can it go from some VM subsystem activity ? I have 16M of RAM in my box
and I runned lmbench with 8M maximal buffer size. The latency grows
with the size of buffer.  Is it possible that when
the size of buffer grows the VM subsystem moves the non-recently used
pages to some pool and when they are accessed again it gets the VM fault
and remaps them back to that process?

Thanks!

-SB