I've spent several years optimizing a specialized IPC mechanism for a work project. I've spent time reviewing the Linux Kernel's unix socket source code to understand obscure edge cases. There isn't really much to optimize - it's just copying bytes between buffers. Most of the complexity of the code has to do with permissions and implementing the ability to send file descriptors. All my benchmarks have unambiguously showed unix sockets to be more performant than loopback TCP for my particular use case.

I agree, but practically speaking they're used en masse all across the field and people did bother to make them good [enough]. I suspect the benchmarks where they come up equal are cases where things are limited by other factors (e.g. syscall overhead), though I don't want to make unfounded accusations :)

Ok, now it sounds like you're blaming unix sockets for someone's shitty code...

No idea what "TI Envelope" is, and a Google search doesn't come up with usable results (oh the irony...) - if it's a logging/metric thing, those are hard to get to perform well regardless of socket type. We ended up using batching with mmap'd buffers for crash analysis. (I.e. the mmap part only comes in if the process terminates abnormally, so we can recover batched unwritten bits.)

I'm a xoogler so I don't have access. Do you have a TL;DR that you can share here (for non-Googlers)?