3 ms·

How would you suggest the kernel would accomplish that feat? If the user calls read() on a file descriptor, what can the kernel do except... you know... actuall

• Someone 4y ago
  It _could_ look at the instructions following the read call and do a sort of high-level software macro-op fusion (https://en.wikichip.org/wiki/macro-operation_fusion https://en.wikichip.org/wiki/macro-operation_fusion) That already would be going beyond the duty for a jitting virtual machine, so I don’t think you can expect that from a CPU. I also likely would make lots of programmers uneasy if their OS does that sort of thing. For a ‘real’ CPU, I also fear handling all the edge cases would be horrific (the program may do a read-write pair of calls, but how do you ascertain it doesn’t read that data later? What if the read call tries to read into unwritable memory? What if the program is being traced, and read calls are being logged? Etc)
• ape4 4y ago
  I know it wouldn't be easy. But the goal could be to let users write simple programs that say what they mean. Since many programs do: while(!eof) { read(); write(); } that could be optimized similar to the way a compiler optimizes known idioms. Perhaps it could notice a well know sequence of calls and avoid userspace/kernels space copies. But, yeah, very non-trivial.