On Sun, 16 Sep 2007 23:43:40 -0700 Andrew Morton <[EMAIL PROTECTED]> wrote:
> On Sun, 16 Sep 2007 17:02:46 -0700 (PDT) [EMAIL PROTECTED] wrote: > > > http://bugzilla.kernel.org/show_bug.cgi?id=9031 > > > > Summary: TPC window is to cautious on send > > Product: Networking > > Version: 2.5 > > KernelVersion: Any > > Platform: All > > OS/Version: Linux > > Tree: Mainline > > Status: NEW > > Severity: normal > > Priority: P1 > > Component: IPV4 > > AssignedTo: [EMAIL PROTECTED] > > ReportedBy: [EMAIL PROTECTED] > > > > > > This has been a longstanding "bug" of sorts when talking to a system that > > has > > extremely small windows (under 1.5k). > > > > The only way to give the stack on the other side a nudge is to ACK twice. > > > > Here is a sample transcript, with a max window size of 1025 bytes. > > > > 18:25:43.968358 IP dr.ea.ms.http > 192.168.80.2.40246: . 37377:37633(256) > > ack > > 120 win 5840 > > 18:25:43.992402 IP 192.168.80.2.40246 > dr.ea.ms.http: . ack 37121 win 769 > > <mss > > 256> > > 18:25:44.390305 IP 192.168.80.2.40246 > dr.ea.ms.http: . ack 37121 win 1025 > > <mss 256> > > 18:25:44.823084 IP dr.ea.ms.http > 192.168.80.2.40246: . 37633:37889(256) > > ack > > 120 win 5840 > > > > If I take the "nudge" code out of my IP stack, it sits for an aweful long > > time, > > waiting on the next packet, when there clearly is room for a few more. > > > > Should I: > > 1: Have my IP stack lie about the window till it is important? > > 2: Something else? > > > > I can't see any good reason for the large delay, since it is on a serial > > link, > > via SLIP. > > > > I can point you to source code that will allow you to verify the problem for > > yourself, if you would like. > > See my comment, on bug report, Linux is doing Silly Window Syndrome avoidance (RFC 813) as required in host requirements RFC1122 4.2.3.4 When to Send Data A TCP MUST include a SWS avoidance algorithm in the sender. A TCP SHOULD implement the Nagle Algorithm [TCP:9] to coalesce short segments. However, there MUST be a way for an application to disable the Nagle algorithm on an individual connection. In all cases, sending data is also subject to the limitation imposed by the Slow Start algorithm (Section 4.2.2.15). The Linux mechanism to disable Nagle is setsockopt(TCP_NODELAY). -- Stephen Hemminger <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
