Messages in this thread |  | | | Date | Tue, 27 Oct 1998 21:00:33 +1100 | | From | Richard Gooch <> | | Subject | [OFFTOPIC] UltraSparc MMU problems |
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Hi, all. I've noticed something strange with some UltraSparc machines here, and I don't know if it's silliness in Solaris or in the Ultra itself.
Basically, I have a volume rendering application that bangs on the memory subsystem quite a bit. Typical rendering times for my dataset are around 6 seconds. If I stop using the renderer and fire up another programme which manipulates an array larger than physical memory (hence paging out code and data used in the renderer), quit that programme and use the renderer again (after waiting for it's code and data to page back in), the times go down to 4.9 seconds! Repeated renders give the same time.
If I then exit the renderer and start it again, the times go back up to around 6 seconds. Repeated renders also give the same time. I can repeat the whole procedure of paging out the renderer and I get the same results. This suggests that somehow the rendering times are sensitive to the physical location of pages in RAM or the degree of fragmentation. To my thinking, this shouldn't happen, and makes me suspect either the OS or a defective implementation of the MMU. Actually, I don't see what the OS has to do with it, since once my pages are in RAM, it should have nothing to do with it. So that leaves the MMU.
I don't expect that cache issues should be significant here, since the dataset is much larger than cache (the volume is 13 MBytes). So that leaves the MMU as my main suspect, although that seems unreal.
Is this something our UltraSparc gurus could comment on? Is it Solaris, the MMU or something else?
System is an Ultra 170E with 64 MBytes of RAM.
Regards,
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