| Horizon68 <horizon@horizon.com>: Feb 04 01:18PM -0800 Hello, About SC and TSO and RMO hardware memory models.. I have just read the following webpage about the performance difference between: SC and TSO and RMO hardware memory models I think TSO is better, it is just around 3% ~ 6% less performance than RMO and it is a simpler programming model than RMO. So i think ARM must support TSO to be compatible with x86 that is TSO. Read more here to notice it: https://infoscience.epfl.ch/record/201695/files/CS471_proj_slides_Tao_Marc_2011_1222_1.pdf About memory models and sequential consistency: As you have noticed i am working with x86 architecture.. Even though x86 gives up on sequential consistency, it's among the most well-behaved architectures in terms of the crazy behaviors it allows. Most other architectures implement even weaker memory models. ARM memory model is notoriously underspecified, but is essentially a form of weak ordering, which provides very few guarantees. Weak ordering allows almost any operation to be reordered, which enables a variety of hardware optimizations but is also a nightmare to program at the lowest levels. Read more here: https://homes.cs.washington.edu/~bornholt/post/memory-models.html Memory Models: x86 is TSO, TSO is Good Essentially, the conclusion is that x86 in practice implements the old SPARC TSO memory model. The big take-away from the talk for me is that it confirms the observation made may times before that SPARC TSO seems to be the optimal memory model. It is sufficiently understandable that programmers can write correct code without having barriers everywhere. It is sufficiently weak that you can build fast hardware implementation that can scale to big machines. Read more here: https://jakob.engbloms.se/archives/1435 Thank you, Amine Moulay Ramdane. |
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