Front page | perl.perl5.porters |
Postings from January 2022
On Mon, Jan 17, 2022 at 10:15:33PM +0000, Paul "LeoNerd" Evans wrote:
[lots of benchmarking stuff]
I'm going to have to respectfully disagree with your benchmarking results
and conclusions for populating @_ :-).
First off, I think (if I am reading your diffs correctly), you have
missed cutting out all the @_ tearing down at sub exit that appears
in Perl_cx_popsub_args().
But more generally, note that perl already has a mechanism for calling a
sub without populating @_: the &foo; calling convention. This is already
special-cased in pp_entersub and elsewhere with the hasargs and CxHASARGS
flags. So it should be possible (in theory) to exploit the existing non-@_
entry and exit code paths without adding extra overhead.
Since this pathway already exists, it's possible to benchmark it without
hacking the perl interpreter itself:
use Benchmark ':all';
use feature 'signatures';
no warnings 'experimental';
sub foo0 { }
sub foo2 ($x,$y) { }
cmpthese(-3, {
ampersand => sub { &foo0; },
args0 => sub { foo0(); },
args2 => sub { foo2(1,2); },
});
with that I get:
Rate args2 args0 ampersand
args2 15642116/s -- -64% -69%
args0 43208035/s 176% -- -14%
ampersand 50372768/s 222% 17% --
converting that into microseconds per call, I get
0.1985199622145 ampersand
0.2314384350040 args0
0.6392996957700 args2
that seems to me to show that about 0.033 us is spent per call just setting
up and tearing down @_ itself, even in the absence of any arguments. That
represents about 5% of the total overhead of calling a 2-arg signature
sub.
But it is important to note that signature sub arg processing is NOT yet
optimised. It's always been my long-term plan that the current arrangement
of an OP_ARGELEM (plus nextstate) per arg will be replaced (by the
peephole optimiser) by a single OP_SIGNATURE op which implements a simple
FSM to populate all args. This will be much faster than the current
arrangement. When that comes to pass, the overhead of populating @_ will
then represent considerably more than 5% of the total sub calling overhead.
--
Music lesson: a symbiotic relationship whereby a pupil's embellishments
concerning the amount of practice performed since the last lesson are
rewarded with embellishments from the teacher concerning the pupil's
progress over the corresponding period.
Thread Previous
|
Thread Next