1) Because splice(2) requires either the source or sink to be a pipe. The source is a regular file so the sink has to be a pipe.
2) Because the example Rust program(s), emulating yes(1), had no [simple] way to measure throughput except by piping to another program. We can't fairly compare program A that writes directly to /dev/null with program B that writes to a pipe even if program A can measure its throughput.
2a) What jwilk said.
3) For some reason I thought that glibc had optimizations to elide fwrites to /dev/null, and some of my code was using stdio (e.g. for the final trailing bytes less than the pagesize). I could've sworn either glibc or bash did this, but I can't find any mention of it, now. I realize it would be crazy difficult and ugly for glibc to do this (because of dup2, etc), but glibc does alot of crazy things, and in any event I didn't bother checking beforehand.
Mostly it comes down to fairly comparing benchmarks and kernel facilities. Otherwise, yes, those would be classic examples of Useless Use of Cat.
2) Because the example Rust program(s), emulating yes(1), had no [simple] way to measure throughput except by piping to another program. We can't fairly compare program A that writes directly to /dev/null with program B that writes to a pipe even if program A can measure its throughput.
2a) What jwilk said.
3) For some reason I thought that glibc had optimizations to elide fwrites to /dev/null, and some of my code was using stdio (e.g. for the final trailing bytes less than the pagesize). I could've sworn either glibc or bash did this, but I can't find any mention of it, now. I realize it would be crazy difficult and ugly for glibc to do this (because of dup2, etc), but glibc does alot of crazy things, and in any event I didn't bother checking beforehand.
Mostly it comes down to fairly comparing benchmarks and kernel facilities. Otherwise, yes, those would be classic examples of Useless Use of Cat.