Windows 10: Slow memory allocation on Windows

Hi, I have implemented a program and found out that the performance of allocation a lot of memory is severely limited on Windows. Allocating and reusing a single chunk of memory (10 MB) is actually fast, but initializing a lot of new memory (30 GB) is very slow and surprisingly, the performance degrades increasing the number of threads allocating the memory. The same code compiled with the same compiler settings (g++ -O2) runs 2 to 8 times faster on Ubuntu on the same hardware. Compiling with VS2015 or gcc does not make a difference on Windows (hence I am asking here and not in a programming forum). I thought that Windows is crippling the AMD performance under contract for Intel, but Ubuntu outperforms Windows also with the Intel chips, although not to the same extent.


The pseudo-code is essentially:

for 8 or 32 threads in parallel

allocate and initialize "30 GB divided by the number of threads", in blocks of 10 MB

measure the initialization time here

for 8 or 32 threads in parallel

write new data into the same place that it has initialized above

measure the memory reuse time here


Here is the complete code in C++: https://www.dropbox.com/s/bsjj8b5oqm1noxg/HeapSpeed.cpp?dl=0


Here are the timings for initializing 30 GB of memory on the heap (64 GB RAM available on the PC):


- AMD Threadripper 16 cores with hyperthreading, quad-channel DDR4 (theoretical memory bandwidth should be about 80 GB/s)


Memory initialization with 8 threads:

Windows: 3 GB/s (bad!)


Ubuntu: 14 GB/s


Memory initialization with 32 threads:


Windows: 2.5 GB/s (bad!)


Ubuntu: 21 GB/s



Memory reuse with 8 threads:

Windows: 29 GB/s


Ubuntu: 27 GB/s


Memory reuse with 32 threads:


Windows: 26 GB/s


Ubuntu: 26 MB/s



- Intel i7 4 cores with hyperthreading, quad-channel DDR3 (theoretical memory bandwidth should be about 25.6 GB/s)


Memory initialization with 8 threads:

Windows: 9 GB/s (bad!)


Ubuntu: 17 GB/s



Memory reuse with 8 threads:

Windows: 32 GB/s (bad!)


Ubuntu: 40 GB/s



Is it possible to tweak the Windows settings to match the Ubuntu performances? Or are there specific compiler options for fast memory initialization? Or are there specific functions for threaded allocations? (the Parallel Patterns Library did not help)


Many thanks!

:)

 

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