Re: Any idea about what makes Emacs slow reading on pipes?

[Richard Stallman]

    That is because emacs is using a pty by default for process i/o (I
    guess that is to avoid buffering output from the writer, so emacs will
    get a more steady flow of input to process, e.g. for compiler output),

I am not sure any more what the context is, but the usual reason for
using a pty is so that process groups and associated signals work.