Date: Sun, 1 Jul 2001 01:09:30 -0700 From: "Ted Mittelstaedt" <tedm@toybox.placo.com> To: "David Leimbach" <dleimbac@earthlink.net>, <questions@FreeBSD.ORG> Subject: RE: Real numbers on why loopback is slow in FreeBSD please read... Message-ID: <001801c10205$27b12f60$1401a8c0@tedm.placo.com> In-Reply-To: <20010630112406.A1143@mutt.home.net>
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>-----Original Message----- >From: owner-freebsd-questions@FreeBSD.ORG >[mailto:owner-freebsd-questions@FreeBSD.ORG]On Behalf Of David Leimbach > [rant deleted] >I noticed the really horribly poor latency of FreeBSD when using >the loopback. > >Here are some numbers: >[From the perf MPI test on FreeBSD ] > [numbers deleted, refer to previous message] >So I think I have valid reason to be worried. This is just a ping-pong >test that perf runs but the message latency on linux is more desirable >than FreeBSD. > >Is this related to proc speeds at all? If so how much? > >I would like to do better than 223.44 ms latency for a 0 data length packet >in FreeBSD. > >Any ideas?? > Dave, There's probably another reason that people aren't really paying attention to your posting - they aren't seeing the same figures. Here's the output on my own home system, a Pentium 166Mhz: mail# ping -s 4096 -f 127.0.0.1 PING 127.0.0.1 (127.0.0.1): 4096 data bytes .^. --- 127.0.0.1 ping statistics --- 2574 packets transmitted, 2573 packets received, 0% packet loss round-trip min/avg/max/stddev = 0.235/0.252/0.438/0.013 ms mail# As you can see, with a packetsize of 4096 (8192, your largest size, isn't valid for ping) pinging the loopback as fast as possible, I'm only seeing an average of 252 microseconds, not 400 microseconds as you posted. Doing the same thing again with a packetsize of 64 shows the following: mail# ping -s 64 -f 127.0.0.1 PING 127.0.0.1 (127.0.0.1): 64 data bytes .^C --- 127.0.0.1 ping statistics --- 2995 packets transmitted, 2994 packets received, 0% packet loss round-trip min/avg/max/stddev = 0.071/0.075/0.229/0.004 ms mail# Now I'm seeing only 75 microseconds average. Once again, this is vastly different than the 200+ microseconds your seeing on your test. Now, you said in your posting that your perf stats run a ping pong test so whatever your running ought to be identical to "ping -f -s somedatasize". You didn't post how fast the CPU of your system is, nor any of the other particulars. And, you certainly didn't post the code that your using to generate your numbers. Would you consider the possibility that your code that you wrote to do this is horribly inefficient, instead of FreeBSD? I have observed that most of the problems that people have troubleshooting is when they start assuming that what they have done couldn't possibly have a problem, so they waste all kinds of time searching for the problem that they are convinced that something else has. You need to consider that your code is faulty and test this hypothesis with other people's code that does the same thing. If your code and everyone else's code running on FreeBSD all come up with the same numbers, that are repeatable on other people's system, then we would get interested. But as of now I have attempted to duplicate your hypothesis of inefficient loopback performance under FreeBSD and found that there is no basis for it. Ted Mittelstaedt tedm@toybox.placo.com Author of: The FreeBSD Corporate Networker's Guide Book website: http://www.freebsd-corp-net-guide.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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