From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rick Jones Subject: Is keepalive behaving as expected in 3.7.0+/net-next? Date: Fri, 21 Dec 2012 14:05:28 -0800 Message-ID: <50D4DD28.30903@hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit To: netdev@vger.kernel.org Return-path: Received: from g1t0027.austin.hp.com ([15.216.28.34]:12411 "EHLO g1t0027.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751417Ab2LUWF3 (ORCPT ); Fri, 21 Dec 2012 17:05:29 -0500 Received: from g1t0039.austin.hp.com (g1t0039.austin.hp.com [16.236.32.45]) by g1t0027.austin.hp.com (Postfix) with ESMTP id 29D6438131 for ; Fri, 21 Dec 2012 22:05:29 +0000 (UTC) Received: from [16.103.148.51] (tardy.usa.hp.com [16.103.148.51]) by g1t0039.austin.hp.com (Postfix) with ESMTP id E48E0341A4 for ; Fri, 21 Dec 2012 22:05:28 +0000 (UTC) Sender: netdev-owner@vger.kernel.org List-ID: I was looking to do a bit more documentation clean-up and thought I would work on the descriptions of the "keepalive" sysctls, but first I wanted to see if they behaved as the existing descriptions suggested: > tcp_keepalive_time - INTEGER > How often TCP sends out keepalive messages when keepalive is enabled. > Default: 2hours. > > tcp_keepalive_probes - INTEGER > How many keepalive probes TCP sends out, until it decides that the > connection is broken. Default value: 9. > > tcp_keepalive_intvl - INTEGER > How frequently the probes are send out. Multiplied by > tcp_keepalive_probes it is time to kill not responding connection, > after probes started. Default value: 75sec i.e. connection > will be aborted after ~11 minutes of retries. I interpreted all that that as: When a connection is idle, TCP will send a keepalive probe every tcp_keepalive_time seconds. If a response to a keepalive probe is not received, TCP will resend (retransmit) it every tcp_keepalive_intvl seconds. However, what I see is that on a connection where the remote is indeed still there, only the first keepalive probe is sent after tcp_keepalive_time, and thereafter it is sent every tcp_keepalive_intvl seconds. Now, some of this may relate to my being impatient - rather than wait two hours for the first probe, I set tcp_keepalive_time to 3 seconds, and tcp_keepalive_intvl to 7 seconds. I then kicked-off a ./configure --intervals-enable netperf TCP_RR test with a burst of one and a wait time of 90 seconds and got the following (trimmed) trace: 13:43:46.879133 IP netnextraj.43054 > netnextraj2.srvr: Flags [S], seq 807869796, win 14600, options [mss 1460,sackOK,TS val 133470 ecr 0,nop,wscale 7], length 0 13:43:46.880091 IP netnextraj2.srvr > netnextraj.43054: Flags [S.], seq 1522345902, ack 807869797, win 14480, options [mss 1460,sackOK,TS val 136186 ecr 133470,nop,wscale 4], length 0 13:43:46.880114 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack 1, win 115, options [nop,nop,TS val 133470 ecr 136186], length 0 13:43:46.880306 IP netnextraj.43054 > netnextraj2.srvr: Flags [P.], seq 1:11, ack 1, win 115, options [nop,nop,TS val 133470 ecr 136186], length 10 13:43:46.880948 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack 11, win 905, options [nop,nop,TS val 136187 ecr 133470], length 0 13:43:46.880964 IP netnextraj2.srvr > netnextraj.43054: Flags [P.], seq 1:11, ack 11, win 905, options [nop,nop,TS val 136187 ecr 133470], length 10 13:43:46.881161 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack 11, win 115, options [nop,nop,TS val 133470 ecr 136187], length 0 The first probe above comes after 3 seconds - tcp_keepalive_time - at 13:43:49 13:43:49.886752 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack 11, win 115, options [nop,nop,TS val 134222 ecr 136187], length 0 And it does seem to elicit a response: 13:43:49.887530 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack 11, win 905, options [nop,nop,TS val 136938 ecr 133470], length 0 Now it starts sending probes every 7 seconds (tcp_keepalive_intvl): 13:43:56.903576 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack 11, win 115, options [nop,nop,TS val 135976 ecr 136938], length 0 13:43:56.904480 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack 11, win 905, options [nop,nop,TS val 138693 ecr 133470], length 0 13:44:03.910744 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack 11, win 115, options [nop,nop,TS val 137728 ecr 138693], length 0 13:44:03.911623 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack 11, win 905, options [nop,nop,TS val 140444 ecr 133470], length 0 I;ve deleted the next 9 or so probes... It continues, and doesn't terminate the connection, so I assume it was happy with the responses to the probes. 13:45:13.990746 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack 11, win 115, options [nop,nop,TS val 155248 ecr 156213], length 0 13:45:13.991578 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack 11, win 905, options [nop,nop,TS val 157965 ecr 133470], length 0 Now the next netperf transaction happens: 13:45:16.879222 IP netnextraj.43054 > netnextraj2.srvr: Flags [P.], seq 11:21, ack 11, win 115, options [nop,nop,TS val 155970 ecr 157965], length 10 13:45:16.880033 IP netnextraj2.srvr > netnextraj.43054: Flags [P.], seq 11:21, ack 21, win 905, options [nop,nop,TS val 158687 ecr 155970], length 10 13:45:16.880220 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack 21, win 115, options [nop,nop,TS val 155970 ecr 158687], length 0 But the next keepalive probe is tcp_keepalive_intvl seconds after the last one, rather than that many, or tcp_keepalive_time seconds after the connection was last "active." 13:45:20.998739 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack 21, win 115, options [nop,nop,TS val 157000 ecr 158687], length 0 13:45:20.999754 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack 21, win 905, options [nop,nop,TS val 159717 ecr 155970], length 0 13:45:28.006747 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack 21, win 115, options [nop,nop,TS val 158752 ecr 159717], length 0 13:45:28.007624 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack 21, win 905, options [nop,nop,TS val 161469 ecr 155970], length 0 Is this the expected behaviour? If I reverse the values - make tcp_keepalive_time 7 and tcp_keepalive_intvl 3, it seems that all the probes are after 7 seconds. rick jones