> but I've seen some compelling arguments that a relaxed model doesn't necessarily have much of a benefit, "ELI5" oversimplified explanation why this is insane

> but I've seen some compelling arguments that a relaxed model doesn't necessarily have much of a benefit, "ELI5" oversimplified explanation why this is insane and can be no other way: You write A (not in cache), you write B, you write C, ... you write Y, you read Z (in L1d). In ARM, when A misses L1d, L2, and L3, you can issue writes to B..Y, and the read of Z (which hits in 2 cycles) and go on your merry way, your pipeline sure of the value of Z. With TSO you CANNOT allow the writes to B..Y to be seen by anyone before A, because everyone expects to only see them after A, so you either buffer them or, eventually, sit on your proverbial ass and wait for A to drain. You might have the buffers to put off the consequences for a while, but that is explicitly a cost ARM lacks, AND(this one hurts the most) you can't simply let the load of Z become an architecturally committed observation before A is done. You can speculate it, but you have to preserve the TSO ordering constraints. Eventually you'll run out of write-buffer slots or other resources, or find that your guess of Z's value was ... wrong. This is an example of how TSO loses perf compared to relaxed. The list of how it gains perf compared to relaxed is shorter: { } So, in some cases TSO is the same perf as relaxed, in no cases it is faster, in some cases it is slower. So it must be slower overall, since "overall" is a weighted mix of those. "By how much" is a question of detail and workload. However, unless your workload miraculously never suffers a cache miss while a later instruction hits, TSO must be slower. :)