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Date: Sat, 4 Aug 2012 16:45:33 +0200 From: Sławek Janecki <janecki@...il.com> To: linux-kernel@...r.kernel.org Subject: TCP Delayed ACK in FIN/ACK I have a node.js client (10.177.62.7) requesting some data from http rest service from server (10.177.0.1). Client is simply using nodejs http.request() method (agent=false). Client is on Ubuntu 11.10 box. Why client sends FIN ACK after 475ms? Why so slow? He should send FIN ACK immediately. I have many situations like this. About 1% of whole traffic is request with delayed FIN ACK. Cpu idle on the client is about 99%, so nothing is draining CPU. How to debug this? What could it be? Is there any sysctl option I need to tune? I think this behaviour is the Delayed ACK feature of RFC1122 TCP stack. Link to tcpdump picture (done on a client machine) : http://i48.tinypic.com/35cpogx.png Can you tell why kernel delayed that FIN/ACK. In tcpflow data there is exacly one ACK per packet comming from server. Why kernel delayed client FIN/ACK. It could avoid sending ACK every 'data' packet. But it choose to delay FIN/ACK? Is this possible? Is this a bug? I've also posted question on stackexchange: http://stackoverflow.com/questions/11711218/client-sends-delayed-fin-ack-500ms-to-server Please help. -- pozdrawiam Sławomir Janecki -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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