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DragonFly kernel List (threaded) for 2005-07
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Re: net.inet.tcp.inflight_enable

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Fri, 8 Jul 2005 14:31:53 -0700 (PDT)

:> Sorry, actually, I always set net.inet.tcp.inflight_enable to zero
:> both on DragonFlyBSD and FreeBSD in my experiences (I know it is zero
:> on DragonFlyBSD by default, but I want to make it sure), because
:> unfortunately it reduces throughput in my experiences in an unexpected
:> way.
:I'd like to show an example where TCP throughput was reduced by
:setting net.inet.tcp.inflight_enable=1.
:  http://www.demizu.org/~noritosi/memo/2005/0706/
:The first graph shows a TCP behavior when net.inet.tcp.inflight_enable=0.
:Since congestion window grows exponentially, it took 5 RTTs (about 100ms)
:to send 64KB data.
:The second graph shows a TCP behavior when net.inet.tcp.inflight_enable=1.
:Since congestion window is almost unchanged, it took 14 RTTs (about 300ms)
:to send 64KB data.
:When I sent larger data, the difference became much larger.
:(e.g., 167ms and 1330ms when I sent 512KB data.  RTT=20ms)
:(Note: according to the graphs,
: "cwnd = 3 * 2^RTT" vs. "cwnd = 3 + RTT/N (N is about 10?)")
:Noritoshi Demizu

    Try increasing net.inet.tcp.inflight_stab from 20 to 40 and
    see if that fixes ethe congestion window expansion problem.  I'm
    not sure why the congestion window isn't expanding.

					Matthew Dillon 

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