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Date: Fri, 4 Jun 2010 15:58:57 +0900 From: Ryousei Takano <ryousei@...il.com> To: Ivan Novick <novickivan@...il.com> Cc: netdev@...r.kernel.org Subject: Re: 200 millisecond timeouts in TCP On Fri, Jun 4, 2010 at 7:37 AM, Ivan Novick <novickivan@...il.com> wrote: > Hello, > > Using tcpdump and systemtap I am seeing that sometimes retransmission > of data is sent after waiting 200 milliseconds. However sometimes > retransmissions happen quicker. > > Is there a specifc event that causes these 200 milisec delays to kick > in? Are those events identifiable in netstat -s output? > > Also do you know if the timeout numbers for TCP are configurable parameters? > The minimum RTO value is fixed to 200 ms. It is useful to make the min/max RTO values tunable. For example, reducing the minimum RTO value is effective for TCP incast problem [1]. Of course, it may occur spurious retransmissions. [1] Vijay Vasudevan, et al, Safe and Effective Fine-grained TCP Retransmissions for Datacenter Communication, SIGCOMM2009 In Solaris, there are two tunable parameters: tcp_rexmit_interval_min/max. Do you have plan to introduce sysctl parameters like these to the Linux. Thanks, Ryousei > I am testing on RHEL5 with this kernel: 2.6.18-164.15.1.el5. > > Cheers, > Ivan Novick > -- > 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 > -- 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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