3 ms·

Ooooh interesting. Any more info about the difference in models and how it causes this effect?

• jeffbee 6y ago
  Quick explanation: https://www.cs.utexas.edu/~bornholt/post/memory-models.html https://www.cs.utexas.edu/~bornholt/post/memory-models.html Basically, although I'm sure someone will shout me down for this, x86 provides something close to sequential consistency among loads and stores even for concurrent programs, whereas ARM and POWER provide almost no kind of order for loads and stores without barriers. High-level languages like C++ do not really hide this problem. It is very easy to write a concurrent C++ program on x86 that appears to work in practice but never works on ARM.
  • my123 6y ago
    You need proper memory model handling for the program to be compliant even for x86. If you do it otherwise and you see that it works for you, keep in mind that the compiler is allowed to reorder in that case, which can result in very odd breakage. On x86, sequential consistency isn't the implemented memory model, but rather total store ordering. Stores are buffered inside the core and the guarantee provided is that they'll appear to other cores in the proper order. On SC designs, all the cores have the same view of coherent memory all the time. In such a design, barriers aren't required and are lowered down to NOPs. (only general-purpose processors that I know of that implement sequential consistency are NVIDIA's Tegra K1 (64-bit variant) and Tegra Xavier)