Hi Richard, >> So what is the behaviour when you explicitly select a specific CPU? > > Selecting a specific cpu selects the specific architecture that the cpu > supports, does it not? Thus the architecture example above still applies. > > Unless I don't understand what distinction that you're making?
When you select a CPU the goal is that we optimize and schedule for that specific microarchitecture. That implies using atomics that work best for that core rather than outlining them. >> I'd say that by the time GCC10 is released and used in distros, systems >> without >> LSE atomics would be practically non-existent. So we should favour LSE >> atomics >> by default. > > I suppose. Does it not continue to be true that an a53 is more impacted by > the > branch prediction than an a76? That's hard to say for sure - the cost of taken branches (3 in just a few instructions for the outlined atomics) might well affect big/wide cores more. Also note Cortex-A55 (successor of Cortex-A53) has LSE atomics. Wilco
