Greetings, On 03/12/2007, Stephen Hemminger <[EMAIL PROTECTED]> wrote: > On Mon, 3 Dec 2007 15:59:23 -0800 > "Shao Liu" <[EMAIL PROTECTED]> 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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
