$ dd bs=1M count=10 </dev/urandom >random_file
10485760 bytes (10 MB, 10 MiB) copied, 0.183075 s, 57.3 MB/s

$ clang -O3 cp_x.c -o cp_x

$ time ./cp_x random_file random_file_copy

Can we get any insights from strace?
$strace ./cp_x random_file random_file_copy

===cp command
real    0m0.076s
user    0m0.004s
sys     0m0.008s

====cp_fgetc (stdio)

real    0m0.118s
user    0m0.060s
sys     0m0.037s

====cp_libc_one_byte (read/write)
  
real    7m29.977s
user    0m6.752s
sys     1m24.303s

====cp_libc (read/write) 4096 bytes