I recently had cause to sort a piddle inplace, but it looks like PDL::Ufunc::qsort is not inplace aware.
my $pdl = sequence(10)->rotate(1);
print $pdl, "\n";
I added Inplace=>1 to the pp_def for qsort and qsortvec, and tests for each.
Diff against latest repository is attached.
PDL 2.4.11, Perl 5.14.2, Ubuntu 12.04 kernel 3.2.0-26 x86_64