My program on linux got a drastic speed increase when I wrote fcntl(fd, F_SETPIPE_SZ, size). fd is a pipe to a child process I created with fork+execv. I raised the pipe from 64K to 1MB which seems to be linux max without root permission.
I wrote a test to see how big it is on mac, it's also 64K, but I can't seem to figure out how to increase the pipe size. Does anyone know? I'm using an M2 and ventura
As far as I know macOS doesn't have a similar option available. However if your end goal is to speed up your program, it might be worth taking a closer look at why increasing the pipe capacity on Linux improves performance, as it seems to indicate some underlying problem elsewhere in the program.
An example off the top of my head: if you are sending large chunks of data (>64K), it may be that the reading part of the code doesn't correctly handle truncated data and hangs for some amount of time when a partial chunk is read. With a small buffer this would happen more often, so increasing the buffer size would improve performance, but wouldn't actually fix the root problem.