Memcpy slow compared to manual copy of data

[pascallj]

[pascallj]

Think I got at least one problem figured out. If copy memcpy from into my own code, it results in roughly the same benchmark values as when I adapt my own code to copy 8 instead of 64 bits. So I guess the low memcpy performance comes from the standard C library being in the external dram instead of SRAM.

However I am still wondering why O3 will, instead if optimizing my code for speed, makes my code so much slower.

[sebraa]

Do not execute any code from external memory if you want reasonable performance. Use internal.ldf as linker script.

[pascallj]

[jar]

You can use my shmemx_memcy routine if you need best performance. Nothing else beats it while also handling address misalignment.
https://github.com/USArmyResearchLab/op ... x_memcpy.c

[pascallj]

Thanks! I am using the Parallella board for my bachelor thesis so maybe it is nice to compare the results I finally get with your implementation.

[GreggChandler]

[GreggChandler]

[sebraa]

[DonQuichotte]

Totally agree with sebraa.
Performance is my only goal.
Use internal.ldf or nothing.
Avoid using the libraries as much as possible.
gcc bit handling emulation for example is really poor, I had to replace them with my own (popcount, clz).