11–20 of 62 posts
Aarch64 does indeed have a proper atomic max, but even on x86-64 you can get a wait-free atomic max as long as you only need to support integers up to 64. In that case you can simply do a `lock or` with 1 In most cases it's even better to just store a maximum per thread separately and loop over all threads once to compute the current maximum if you really need it.
Was this compiled at O0? The generated code looks unnecessarily long-winded - at the very least I would expect the match jump table to get culled to only the Relaxed implementation.
RTFA
Hi, author here. My superpower is spending unreasonable amounts of time researching things with no practical purpose. Occasionally I blog about it - as a warning to others.
I liked the article. I saw your PS that we added it to the working draft for c++26, we also made it part of OpenMP as of 5.0 I think. It’s sometimes a hardware atomic like on arm, but what made the case was that it’s common to implement it sub-optimally even on x86 or LL-SC architectures. Often the generic cas loop gets used, like in your lambda example, but it lacks an early cutout since you can ignore any input val…
https://doi.org/10.1145/2486159.2486189 https://jshun.csail.mit.edu/contention.pdf
Did he get the job?