You have to call the run method at the end, once you have declared all the actions that should be performed by the module:

my $pssh = Net::OpenSSH::Parallel->new();

$pssh->add_host($_) for @hosts;
$pssh->push('*', scp_put => '/root/cpu.pl', '/root/');
$pssh->push('*', scp_put => '/root/memory.pl', '/root/');

$pssh->run;
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