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I was playing around with [DSE] again the last day and I noticed that if I specify more than 40 seeds, it gives me warning at the bottom saying something like "may not be useful in a large design" (sorry I don't have the correct warning as on this PC I don't have Quartus installed).
What exactly does it mean by this?
Is it that if you do not meet timing in less than 40 seeds, the design will probably never meet timing.
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The last sentence I quoted is probably the reason for the warning.
I've never noticed that message and probably never tried more than 40 seeds. If DSE actually runs with more than 40, then the results should be valid.
As I mentioned before though, Altera people who know how the Fitter works will say there is usually no need to run more than around 5 seeds, and I rarely run more than 10 because for most designs it is likely that 10 seeds will produce about as good a result as you would ever get. If you need just a few more picoseconds and would rather run a huge seed sweep than change the design, then you might get lucky with a huge number of seeds. For most people though, the best out of 10 seeds will probably be close enough to the best you could possibly get with virtually infinite seeds.
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I'd guess that it means that the set of options called for by the seed would result in significant logic duplication and that for a large design this could result in a no-fit because of running out of resources.
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DSE explorations more complicated than seed sweeps would have different amounts of duplication for the settings tried from one compile to the next. For a simple seed sweep, though, any difference in logic duplication would be entirely in the Fitter and entirely random just like the randomness in the slack results.
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