Сетевой принтер всегда печатает одну копию.

Al ejecutar un comando desde el host al contenedor, el demonio docker lo procesará.

Si exec -it [image ID] bashy luego prueba el tiempo:

$ docker exec -it php bash
root@0fddab587d30:/# time php -i > /dev/null

real    0m0.029s
user    0m0.011s
sys     0m0.018s

Ejecutando straceen el host, a través de dockerd hasta el contenedor

$ strace -c -f -S name docker run -d --rm php:cli php -i > /dev/null
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
  0.04    0.000073           7        10        10 access
  0.01    0.000025          25         1           arch_prctl
  0.04    0.000064          21         3           brk
  0.21    0.000359          45         8           clone
  0.09    0.000158           9        17           close
  0.02    0.000036           9         4         2 connect
  0.02    0.000027          27         1           epoll_create1
  0.04    0.000068          11         6           epoll_ctl
  3.97    0.006676          56       120           epoll_wait
  0.00    0.000000           0         1           execve
  0.03    0.000056          14         4           fcntl
  0.05    0.000082           6        13           fstat
 72.92    0.122754         128       959       161 futex
  0.00    0.000001           1         2           getpeername
  0.00    0.000000           0         1           getpid
  0.01    0.000022          22         1           getrandom
  0.00    0.000000           0         2           getsockname
  0.12    0.000199          22         9           gettid
  0.00    0.000004           4         1           getuid
  0.03    0.000044          22         2         1 ioctl
  0.01    0.000011           6         2           lseek
  0.78    0.001317          20        67           mmap
  0.49    0.000821          24        34           mprotect
  0.25    0.000427          39        11           munmap
  0.01    0.000013          13         1           open
  0.09    0.000154          11        14           openat
  0.02    0.000027          27         1           prlimit64
 17.57    0.029574          78       381           pselect6
  0.10    0.000166           7        23         6 read
  0.03    0.000046          46         1           readlinkat
  1.50    0.002522          20       128           rt_sigaction
  0.74    0.001241           9       132           rt_sigprocmask
  0.02    0.000032          32         1           sched_getaffinity
  0.30    0.000500          18        28           sched_yield
  0.10    0.000175          19         9           set_robust_list
  0.01    0.000025          25         1           set_tid_address
  0.00    0.000000           0         2           setsockopt
  0.19    0.000323          18        18           sigaltstack
  0.03    0.000044          11         4           socket
  0.13    0.000215           8        28        27 stat
  0.03    0.000049          10         5           write
------ ----------- ----------- --------- --------- ----------------
100.00    0.168330                  2056       207 total

Y con la ejecución de strace en el contenedor php:cli, el tiempo es significativamente menor incluso con más llamadas al sistema, parece que la llamada al sistema futexes motivo de preocupación aquí:

$ docker run -it --security-opt seccomp:unconfined php:cli bash
root@3bd1a83a2586:/# apt update && apt install strace

root@3bd1a83a2586:/# strace -c -f -S name php -i > /dev/null
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
  4.38    0.000830          15        55        54 access
  0.03    0.000006           6         1           arch_prctl
  0.00    0.000000           0        15           brk
  2.73    0.000518           8        61           close
  0.00    0.000000           0         1           execve
  3.74    0.000708          12        61           fstat
  0.02    0.000003           0        18           futex
  0.00    0.000000           0         1           getcwd
  0.00    0.000000           0         2           getdents
  0.00    0.000000           0         3           getrandom
  0.00    0.000000           0         2           getrlimit
  0.00    0.000000           0         1         1 ioctl
  0.00    0.000000           0         2           lseek
  0.00    0.000000           0         5         1 lstat
  0.00    0.000000           0         1           madvise
 10.42    0.001974          14       145           mmap
  5.06    0.000959           9       108           mprotect
  0.24    0.000046           4        13           munmap
 10.34    0.001960          28        69         9 open
  3.45    0.000654          10        63           read
  0.00    0.000000           0        80           rt_sigaction
  0.00    0.000000           0         2           rt_sigprocmask
  0.00    0.000000           0         1           set_robust_list
  0.00    0.000000           0         1           set_tid_address
  0.00    0.000000           0         1           socket
  0.23    0.000043           7         6         4 stat
  0.00    0.000000           0         1           sysinfo
  0.00    0.000000           0         1           uname
 59.36    0.011250           4      3037           write
------ ----------- ----------- --------- --------- ----------------
100.00    0.018951                  3757        69 total