Two different threads within a single process can share a common memory location by reading and/or writing to it.
Usually, such (intentional) sharing is implemented using atomic operations using the lock prefix on x86, which has fairly well-known costs both for the lock prefix itself (i.e., the uncontended cost) and also additional coherence costs when the cache line is actually shared (true or false sharing).
Here I'm interested in produced-consumer costs where a single thread P writes to a memory location, and another thread `C reads from the memory location, both using plain reads and writes.
What is the latency and throughput of such an operation when performed on separate cores on the same socket, and in comparison when performed on sibling hyperthreads on the same physical core, on recent x86 cores.
In the title I'm using the term "hyper-siblings" to refer to two threads running on the two logical threads of the same core, and inter-core siblings to refer to the more usual case of two threads running on different physical cores.