Optimizing MAKEOPTS in Gentoo Linux

cat > gen_bench.sh <<'EOF'
#!/bin/sh
set -eu

FILES=${FILES:-64}
FUNCS=${FUNCS:-200}
STEPS=${STEPS:-2000}

rm -f file*.c main.c

f=0
while [ "$f" -lt "$FILES" ]; do
  out="file${f}.c"
  : > "$out"
  printf '%s\n' '#include <stdint.h>' >> "$out"

  i=0
  while [ "$i" -lt "$FUNCS" ]; do
    printf 'uint64_t func_%d_%d(uint64_t x){\n' "$f" "$i" >> "$out"
    printf '%s\n' '  uint64_t a=x^0x9e3779b97f4a7c15ULL;' >> "$out"
    printf '%s\n' '  uint64_t b=(x<<1)|1;' >> "$out"
    printf '%s\n' '  uint64_t c=0xBF58476D1CE4E5B9ULL;' >> "$out"

    s=0
    while [ "$s" -lt "$STEPS" ]; do
      k=$((s & 7))
      printf '  if ((a&7)==%d) { a = (a + b) ^ (a >> 3); }\n' "$k" >> "$out"
      printf '  else { a = (a * c + %dULL) ^ (a << 5); }\n' "$s" >> "$out"
      printf '  b ^= (a + %dULL) * 0x94D049BB133111EBULL;\n' "$s" >> "$out"
      s=$((s+1))
    done

    printf '%s\n' '  return a ^ b;' >> "$out"
    printf '%s\n' '}' >> "$out"
    i=$((i+1))
  done

  f=$((f+1))
done

printf '%s\n' 'int main(void){return 0;}' > main.c
EOF

n=$(nproc)

for j in 1 "$((n/2))" "$n" "$((n+1))" "$((n*2))"; do
  [ "$j" -lt 1 ] && continue
  make clean >/dev/null 2>&1
  printf "jobs=%-3s  " "$j"
  t=$( { TIMEFORMAT=$'real=%3R  user=%3U  sys=%3S'
         time make -j"$j" >/dev/null 2>build.log
       } 2>&1 )
  echo "$t"
done