This is interesting. Guess what effect cpu frequency scaling has on
memcpy. I wonder if the difference has to do purely with the cpu
frequency, or if it's because the memory controller in on the die.
At 1800 MHz:
$ ./memcpy 1808 1000 1048576
Memory to memory copy rate = 1060.210815 MBytes / sec. Block size = 1048576.
At 1000 MHz:
$ ./memcpy 1005 1000 1048576
Memory to memory copy rate = 808.985352 MBytes / sec. Block size = 1048576.
This is an unpatched glibc, of course.
I've got a single 512MB stick of premium Corsair ram in it (the sister
stick lives in another computer until prices drop, at which time I will
buy another matched pair of the good stuff).
The fact that I'm using only one stick and I'm getting speeds similar to
those using two, suggests to me that the strangely low numbers some
people are getting are not explained away by their using only a single
channel.
--
"Pluralitas non est ponenda sine necessitate" - W. of O.
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