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Subject: Memory latency, (was CB sponsors entry of)

Author: David Blackman

Date: 01:28:26 08/13/00

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On August 12, 2000 at 23:37:00, Robert Hyatt wrote:


>I haven't seen _any_ latency improvements since 1995.  Don't get fooled by
>SDRAM and the like streaming memory into the L1 cache.  Write a program
>that addresses words that are scattered randomly over memory.  Then that
>fancy streaming/buffering is worthless and you get a feel for true memory
>latency.  And you'll see that 100us number is pretty close to the truth.

The speed-ups i have seen were measured numbers, not advertising numbers. And i
certainly know there is a big difference. My measurements were genuine latency
for random addressing of large arrays, using pointer chasing to make sure
nothing got hidden in the pipeline. 300 to 1000 ns in 1995. 100 to 200 now. (and
200 is getting rarer). There were probably a few things back in 1995 that could
do 100 but they weren't cheap or easy to find.



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