shell exec is about 30 times slower than raw exec syscall

[X512]

This is hrev57820.

Shell (Bash/Zsh etc.) execution time is very slow compared Linux/*BSD that significantly slow down Autotools based projects compilation and other tasks that heavily use shell scripts. Raw exec syscall is significantly faster (30x). I am not sure is it kernel, libroot or shell port problem, it need more investigation.

UPDATE: problem is related to POSIX locale support. Setting LC_ALL=C significantly speed up shell execution.

loop.sh:

#!sh

if (( $1 <= 0 ))
then
    exit
fi

exec loop.sh $(($1 - 1))

loop.c:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>


int main(int argc, char **argv)
{
    if (argc < 2)
        return 1;

    int n = atoi(argv[1]);
    if (n <= 0)
        return 0;
    
    char buf[32];
    sprintf(buf, "%d", n - 1);
    char *newArgs[3] = {argv[0], buf, NULL};
    execvp(newArgs[0], newArgs);
    
    return 0;
}

time ./loop.sh 1000:

real    0m13.775s
user    0m11.713s
sys     0m1.875s

time ./loop 1000:

real    0m0.409s
user    0m0.144s
sys     0m0.240s

export LC_ALL=C time ./loop.sh 1000:

real    0m1.470s
user    0m0.878s
sys     0m0.546s

[waddlesplash]

For reference, here's what I get for both these benchmarks on Linux (in a VM):

time ./loop.sh 1000

real	0m0.930s
user	0m0.111s
sys	0m0.804s

time ./loop 1000

real	0m0.432s
user	0m0.047s
sys	0m0.373s

[waddlesplash]

And on WSL1 (on the host):

time ./loop.sh 1000

real    0m4.247s
user    0m0.422s
sys     0m2.875s

time ./loop 1000

real    0m1.869s
user    0m0.031s
sys     0m1.031s

[waddlesplash]

hrev57827 may help a little bit here.