Date: Mon, 23 Jun 2008 19:13:55 +1000 From: Jerahmy Pocott <quakenet1@optusnet.com.au> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: freebsd-stable@freebsd.org Subject: Re: Sysctl knob(s) to set TCP 'nagle' time-out? Message-ID: <BFAD9FEC-A15B-4109-AB61-A3B8814898CE@optusnet.com.au> In-Reply-To: <200806230827.m5N8RBlW085475@apollo.backplane.com> References: <0222EAC1-A278-41D2-9566-C9CF19811068@optusnet.com.au> <200806230827.m5N8RBlW085475@apollo.backplane.com>
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On 23/06/2008, at 6:27 PM, Matthew Dillon wrote: > Can it break down and cause excessive lag? Yes, it can. > Interactive > games almost universally have to disable Nagle because the lag is > actually due to the data relay from client 1 -> server then > relaying > the interactive event to client 2. Without an immediate > interactive > response to client 1 the ack gets delayed and the next event from > client 1 hits Nagle and stops dead in the water until the first > event > reaches client 2 and client 2 reacts to it (then client 2 -> > server -> > (abort delayed ack and send) -> client 1 (client 1's nagle now > allows > the second event to be transmitted). That isn't a deadlock, just > really poor interactive performance in that particular situation. Yeah, that's what I'm talking about. True, it's not really a dead-lock, but it's terribly slow! The interaction can cause a 200ms delay on a LAN, as can be seen with samba if you disable tcp_nodelay.. > In anycase, the usual solution is to disable Nagle rather then mess > with delayed acks. What we need is a new Nagle that understands > the > new reality for interactive connections... something that doesn't > break > performance in the 'server in the middle' data relaying case. Exactly, there is nothing really wrong with delayed acks.. But with sysctl I CAN disable and mess with the delayed acks, but I can't seem to do anything to Nagle. That's why I was thinking if I could change the Nagle time-out to 0ms it would effectively disable it.. Cheers. J.
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