To summarise syscalls by time or count, use strace -c. To include child processed, add -f switch. For example:

λ strace -cf git status
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
100.00    0.000008           0       247        24 lstat
  0.00    0.000000           0        48           read
  0.00    0.000000           0         3           write
                     ... list goes on ...