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Open Source and information security mailing list archives
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Date: Mon, 3 Dec 2007 17:23:35 -0800 From: "Lachlan Andrew" <lachlan.andrew@...il.com> To: "Stephen Hemminger" <shemminger@...ux-foundation.org> Cc: shaoliu@...nceton.edu, "David S. Miller" <davem@...emloft.net>, "Herbert Xu" <herbert@...dor.apana.org.au>, "Douglas Leith" <doug.leith@...m.ie>, "Robert Shorten" <robert.shorten@...m.ie>, netdev@...r.kernel.org Subject: Re: [RFC] TCP illinois max rtt aging Greetings, On 03/12/2007, Stephen Hemminger <shemminger@...ux-foundation.org> wrote: > On Mon, 3 Dec 2007 15:59:23 -0800 > "Shao Liu" <shaoliu@...nceton.EDU> wrote: > > And also a question, why the samples when SACK is active are outliers? > > Any sample with SACK is going to mean a loss or reordering has occurred. > So shouldn't the SACK values be useful, but RTT values from retransmits > are not useful. When SACK is active, the per-packet processing becomes more involved, tracking the list of lost/SACKed packets. This causes a CPU spike just after a loss, which increases the RTTs, at least in my experience. This is a separate issue from the fact that it is hard to get RTT measurements from lost/retransmitted packets themselves. Cheers, Lachlan -- Lachlan Andrew Dept of Computer Science, Caltech 1200 E California Blvd, Mail Code 256-80, Pasadena CA 91125, USA Ph: +1 (626) 395-8820 Fax: +1 (626) 568-3603 http://netlab.caltech.edu/~lachlan -- 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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