{n} times faster than C

I'm not so sure that the right take-away is "hand-written assembler is 6x faster than C." It's more like "jumps are a lot slower than conditional arithmetic." And that can [edit:often] be achieved easily in C by simply not using switch statements when an if statement or two will work fine.

Rewriting the C function as follows got a 5.5x speedup:

    int run_switches(char *input) {
        int r = 0;
        char c; 
        while (1) {
            c = *input++;
            if (c == 's') r++;
            if (c == 'p') r--;
            if (c == '\0') break;
        }
        return r;
    }

Results:

    [16:50:14 user@boxer ~/looptest] $ gcc -O3 bench.c loop1.c -o lone
    [16:50:37 user@boxer ~/looptest] $ gcc -O3 bench.c loop2.c -o ltwo
    [16:50:47 user@boxer ~/looptest] $ time ./lone 1000 1
    449000
    ./lone 1000 1  3.58s user 0.00s system 99% cpu 3.589 total
    [16:50:57 user@boxer ~/looptest] $ time ./ltwo 1000 1
    449000
    ./ltwo 1000 1  0.65s user 0.00s system 99% cpu 0.658 total

I believe the first `jne` should be `je`, right ?

Gosh, I'd have to see if I can dig it up this was a few years ago.

I did all of the above, plus profiling (sb-sprof combined with disassemble will show assembly level profiling).

What version of GCC are you using? For me both versions perform the same, both on Ubuntu and Windows:

    $ time ./lone 1000 1
        851000

        real    0m3.578s
        user    0m3.574s
        sys     0m0.004s
        
    $ time ./ltwo 1000 1
        851000

        real    0m3.583s
        user    0m3.583s
        sys     0m0.000s

    $ gcc --version
        gcc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0
        Copyright (C) 2019 Free Software Foundation, Inc.
        This is free software; see the source for copying conditions.  There is NO
        warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

You can also use math to avoid most of the jumps:

    int run_switches(char *input) {
      int res = 0;
      while (true) {
        char c = *input++;
        if (c == '\0') return res;
        // Here's the trick:
        res += (c == 's') - (c == 'p');
      }
    }

This gives a 3.7x speed compared to loop-1.c. The lower line count is also nice.