![]() ![]() Thus to conclude, there is difference between stack and heap allocation strategies, but in real processing life, the affect on processing speed is low. But any way on 1 million loops with 10 allocation+init+free attempts, we see that difference is about 8% at 60KB total processing size. To continue we see that with -O2 filled data initialization shows much smaller gap between stack and heap allocation, due to fact that CPU is much more busy with data processing than allocation procedures. But needs to take into account that 10 millions, is very very big number to process. So if checking on single pair of malloc+free, this will be about 0.4 seconds. Difference is about 4 seconds on 10M loops over 10 allocation attempts. In conclusions we see that pure with out data init, stack allocation is much faster. Heap vs Stack, -O1, no data initġM allocations with 10 mixed blocks Conclusions To slow machine might give “infinite” wait time for results. As too fast machine will give inconsistent measurements. For your hardware setup, you might want to adjust LOOPS variable in build.sh before running, due to different machine speed. Particular test cases was executed on Intel(R) Core(TM) i7-6600U CPU, Linux 64 bit, 4.15.0-50-generic, Spectre and Meltdown patches disabled. The stack based allocation with different sizes is done by using C99 variable length array feature. The actual code used for testing can be found here. The testing package uses Enduro/X high performance middleware standard library for results plotting and time measurements. Thus the test case with initialization uses pre-initialized memory block with random data which is copied to target buffer. The typical memory block usage usually is not byte access, but some more bulky, like mem copy, integer, long, etc i.e. The data initialization is done by doing memcpy. In test cases with out memory initialization, the memory pointer addresses are summed and printed on stderr, so that compiler would optimize the allocations because of no further usage. ![]() Using gcc -O2 optimizations, heap vs stack with data init.Using gcc -O2 optimizations, heap vs stack with out data init. ![]()
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