Re^2: I think I just found a good reason to use backticks in a void context.

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Re^3: I think I just found a good reason to use backticks in a void context. by OfficeLinebacker (Chaplain) on Jan 14, 2007 at 10:05 UTC
Hi, Browser, I saw that; but I saw this in the doc: "NOTE: Unlike the other protocols, the return value does NOT determine if the remote host is alive or not since the full TCP three-way handshake may not have completed yet." So I guess the thing to do would be to ping the hosts outside the loop and then only loop through the hosts that respond? I guess you lose a little bit of timeliness (the whole script takes about 20 seconds to run). So it's possible that when I get to the last machine in my list, I'm working on a ping success value from ~19 seconds ago. Also, a quick benchmark of the syn vs udp protocols (similar to the one where I bm'd backticks vs Net::Ping) actually showed no advantage (some were faster, some were slower) (and that's just the outward leg!): Ping with Net::Ping (syn) took 0.002087 seconds Ping with Net::Ping (udp) took 0.000932 seconds .. Ping with Net::Ping (syn) took 0.000977 seconds Ping with Net::Ping (udp) took 0.001136 seconds .. Ping with Net::Ping (syn) took 0.001145 seconds Ping with Net::Ping (udp) took 0.001183 seconds .. Ping with Net::Ping (syn) took 0.001282 seconds Ping with Net::Ping (udp) took 0.001024 seconds .. Ping with Net::Ping (syn) took 0.001163 seconds Ping with Net::Ping (udp) took 0.001019 seconds .. Ping with Net::Ping (syn) took 0.001049 seconds Ping with Net::Ping (udp) took 0.000696 seconds .. Ping with Net::Ping (syn) took 0.00084 seconds Ping with Net::Ping (udp) took 0.000815 seconds .. Ping with Net::Ping (syn) took 0.000822 seconds Ping with Net::Ping (udp) took 0.000707 seconds .. Ping with Net::Ping (syn) took 0.000956 seconds Ping with Net::Ping (udp) took 0.000822 seconds .. Ping with Net::Ping (syn) took 0.000828 seconds Ping with Net::Ping (udp) took 0.000734 seconds .. Ping with Net::Ping (syn) took 0.000802 seconds Ping with Net::Ping (udp) took 0.000704 seconds .. Ping with Net::Ping (syn) took 0.000835 seconds Ping with Net::Ping (udp) took 0.000821 seconds .. Ping with Net::Ping (syn) took 0.000822 seconds Ping with Net::Ping (udp) took 0.000712 seconds .. Ping with Net::Ping (syn) took 0.000702 seconds Ping with Net::Ping (udp) took 0.000824 seconds .. Ping with Net::Ping (syn) took 0.000823 seconds Ping with Net::Ping (udp) took 0.000719 seconds .. Ping with Net::Ping (syn) took 0.00104 seconds Ping with Net::Ping (udp) took 0.000782 seconds .. Ping with Net::Ping (syn) took 0.000563 seconds Ping with Net::Ping (udp) took 0.000474 seconds It seems to me a better way to test the performance is something like this:(it's late so forgive me if my logic is off) Readonly my $udp_pinger => Net::Ping->new( 'udp', 1 ); Readonly my $syn_pinger => Net::Ping->new( 'syn', 1 ); foreach my $x ( 0 .. 5 ) { #test the syn prot with two loops my $t0 = [ gettimeofday() ]; foreach my $host (@host_list) { $syn_pinger->ping($host) \|\| die "syn ping failed for $host"; } foreach my $host (@host_list) { $syn_pinger->ack($host) \|\| die "syn ack failed for $host"; } my $e0 = tv_interval($t0); print "$e0 seconds to ping $NUM_HOSTS hosts with syn"; #test the udp prot with one loop $t0 = [ gettimeofday() ]; foreach my $host (@host_list) { $udp_pinger->ping($host) \|\| die "udp ping failed for $host"; } $e0 = tv_interval($t0); print "$e0 seconds to ping $NUM_HOSTS hosts with udp"; print "---------------------------"; } ## end foreach my $x ( 0 .. 5 ) [download] (I didn't want to go too crazy with number of iterations, but here's a pretty representative result: 0.015293 seconds to ping 17 hosts with syn 0.013442 seconds to ping 17 hosts with udp --------------------------- 0.013814 seconds to ping 17 hosts with syn 0.013393 seconds to ping 17 hosts with udp --------------------------- 0.01381 seconds to ping 17 hosts with syn 0.01327 seconds to ping 17 hosts with udp --------------------------- 0.014273 seconds to ping 17 hosts with syn 0.013056 seconds to ping 17 hosts with udp --------------------------- 0.014191 seconds to ping 17 hosts with syn 0.013396 seconds to ping 17 hosts with udp --------------------------- 0.016453 seconds to ping 17 hosts with syn 0.013 seconds to ping 17 hosts with udp I suppose a better test would be just just call ack non-specifically the right number of times, and keep track of who's responded. But that seems like a lot of work to save a few milliseconds (yeah, I know--kinda late to be saying that). I'm happy going from 1.008->.008->.005->.0015 seconds per host. I think I've reached the point of diminishing returns. However, if you were checking hundreds or more hosts, I could see where that could be worth it. I like computer programming because it's like Legos for the mind.	[reply] [d/l]
Re^4: I think I just found a good reason to use backticks in a void context. by BrowserUk (Patriarch) on Jan 14, 2007 at 10:33 UTC
I suppose a better test would be just just call ack non-specifically the right number of times, and keep track of who's responded. But that seems like a lot of work to save a few milliseconds (yeah, I know--kinda late to be saying that). I'm happy going from 1.008->.008->.005->.0015 seconds per host. I think I've reached the point of diminishing returns. However, if you were checking hundreds or more hosts, I could see where that could be worth it. I absolutely agree. You've got to need the performance gain to make the extra complexity worth the effort. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]