Date: Sat, 23 Sep 2006 15:28:36 +0100 From: David Malone <dwmalone@maths.tcd.ie> To: Andre Oppermann <andre@freebsd.org> Cc: Andrew Gallatin <gallatin@cs.duke.edu>, alc@freebsd.org, freebsd-net@freebsd.org, freebsd-current@freebsd.org, Robert Watson <rwatson@freebsd.org>, tegge@freebsd.org Subject: Re: Much improved sendfile(2) kernel implementation Message-ID: <200609231528.aa12963@walton.maths.tcd.ie> In-Reply-To: Your message of "Sat, 23 Sep 2006 12:20:01 %2B0200." <45150A51.8080501@freebsd.org>
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> The congestion window is increased based on the ACK's received. TSO > is only done on the send side and only up to the current congestion > window. I have been careful not to get any changes in congestion > control behavior with TSO. (Which does not mean that there may be > other bugs lurking in our congestion control.) I think the reason this happened in Linux was because thw congestion window is counted in segments, which were now TSO sized. You'd send 1 TSO sized segment, get back (say) 10 ACKs because of segmentation and increase the window size by 10*TSO_SEG_SIZE/cwnd insead of 10*REAL_MSS/cwnd. We're unlikely to have exactly the same bug, because we count cwnd in bytes, but it doesn't rule out haveing other unexpected/subtle interactions (like higher varience of RTT esitmation - I guess all packets in a TSO segment are now sent with the same timestamp?). David.
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