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Date: Tue, 20 Jul 2010 00:03:00 +0200 From: Eric Dumazet <eric.dumazet@...il.com> To: Tom Herbert <therbert@...gle.com> Cc: netdev@...r.kernel.org Subject: Re: Very low latency TCP for clusters Le lundi 19 juillet 2010 à 11:44 -0700, Tom Herbert a écrit : > I see about 7 usecs as best number on loopback, so I believe this is > in the ballpark. As I mentioned above, this about "best case" latency > of a single thread, so we assume any amount of pinning or other > customized configuration to that purpose. Well, given I get 29 us on a ping between two machines (Gb link, no process involved on receiver, only softirq), I really doubt we can reach 5 us on a tcp test involving a user process on both side ;) $ ping -f -c 10000 -q 192.168.0.1 PING 192.168.0.1 (192.168.0.1) 56(84) bytes of data. --- 192.168.0.1 ping statistics --- 10000 packets transmitted, 10000 received, 0% packet loss, time 395ms rtt min/avg/max/mdev = 0.029/0.032/0.434/0.010 ms, ipg/ewma 0.039/0.033 ms On loopback, its a bit better of course, but there is no cache miss nor scheduler involved. $ ping -f -c 10000 -q 127.0.0.1 PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data. --- 127.0.0.1 ping statistics --- 10000 packets transmitted, 10000 received, 0% packet loss, time 55ms rtt min/avg/max/mdev = 0.002/0.002/0.015/0.001 ms, ipg/ewma 0.005/0.002 ms -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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