Patterns of locality in xterm

So, I fixed the problem I was having with ranges by reducing the number of times the range was being accessed by something like 1000 orders of magnitude by pushing the calculation to much later on in the program (ie instead of checking the range on every calculation, check it only at the end when some other filtering has already happened).

And so I can now show the world a graph that illustrates how xterm‘s initialisation does indeed show different phases of locality – ie that in a small enough time frame spacial locality is shown in memory accesses, but over a bigger time space that locality will shift – this is important because it indicates that a good virtual memory manager would be able to flush the pages from the old locality out of the system:

locality in xterm memory accessesPlainly I need to do a bit more work on the graphing software – but the yellow lines are the axis and the green dots indicate where the memory is being accessed – time (or rather its analogue in terms of instructions executed) runs from left to right and (process) memory address gets greater as you move from the bottom up.

In fact this graph is only looking at the bottom 10% of the range of memory accessed by the application (and we are ignoring the instructions in favour of explicit heap loads, stores and modifications) – but the problem is that for most of that range nothing is accessed – again I need to adjust the Groovy script to make it better.

None of this is new – this experiment was first conducted in the early 1970s – though I am not aware of anyone having done it for Linux – but I suspect they have.


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