I have no such info in dmsg. I think I will file a issue to Node.js Dev Team. Thanks for reply.
On Sat, Aug 4, 2012 at 6:34 PM, Eric Dumazet <eric.duma...@gmail.com> wrote: > On Sat, 2012-08-04 at 16:51 +0200, richard -rw- weinberger wrote: >> On Sat, Aug 4, 2012 at 4:45 PM, Sławek Janecki <jane...@gmail.com> wrote: >> > 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. >> >> CC'ing netdev. >> > > I see nothing wrong in this tcpdump. You should strace the application > instead. > > FIN/ACK is sent when client closes its socket (or calls shutdown()), and > not in reply of FIN sent by the server. > > Kernel has no additional delay. I suspect your client is slow processing > the server answer, then close() its socket _after_ data processing. > > Its possible tcp_send_fin() has to loop while allocating one skb under > very high memory pressure, and it seems we have no counters for this > case. But if it _was_ ever happening, you would have lot of messages in > kernel log (dmesg) about alloc_skb_clone() failures. > > > -- pozdrawiam Sławomir Janecki -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
