Then i have new results of my investigation ;)
so when i do
# ps aux | grep vzdump
#root 738698 0.0 0.0 204976 38048 ? S Dec23 1:32 /usr/bin/perl -w -T /usr/bin/vzdump
I do a strace on process and i have this result in loop
select(8, [6], NULL, NULL, {1, 0}) = 0...