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Dne 23.9.2009 16:32, Bruno Chareyre napsal(a):
L1 cache is certainly not useless even for DEM, it's just that all your data will not fit inside. But still if one part of your data is at one memory location (not chain of shared_ptr's jumping all over the RAM), it makes the computation much faster (e.g. Dem3Dof classes have comparable speed to SpheresContactGeometry even if they copy extra Vector3r+Quaternionr (=28b of data) at every step. There are some papers [1] on that; speeds of the L1 cache are orders of magnitude higher than speed of CPU-RAM bus and of the RAM modules themselves.Yes, all nodes have this but some of them have bigger cache (reason for the option "big cache") so you don't use RAM at all if possible (but yeah, if its 6MB then it is useless for DEM...).All nodes ARE using internal memory attached to a node. You are confusing something here. Each node is an *ordinary* PC. They are just connected to each other with a mechanism which allows submitting jobs (sun grid engine). There is nothing special about them. Maybe Remi was talking about big CPU cache which is always used automatically. And indeed is relatively big: a whole 6 MB ! Which confirms what I already said, if you don't use RAM then Intels are much faster than AMD (this is the case when you are calculating digits of pi or mandelbrot set, or such). If you do use RAM, then AMDs are faster. In our calculations we use RAM. A smallest simulation uses 100MB. Another simulation could be 1 GB. There is no point with 6 MB of CPU cache then.
Cheers, V. [1] http://people.redhat.com/drepper/cpumemory.pdf
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