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    SubjectRe: [NOT VERY SAFE] [TCP]: Set initial_ssthresh default to zero in Cubic and BIC.
    Dear David

    Actually, tcp_sk(sk)->snd_ssthresh is not initialized,
    if initial_ssthresh is 0.

    The patch should be

    static void bictcp_init(struct sock *sk)
    {
    bictcp_reset(inet_csk_ca(sk));
    - if (initial_ssthresh)
    - tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
    +
    + tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
    }

    Best Regards
    Komuro

    >
    > Dear David
    >
    > The patch "[TCP]: Set initial_ssthresh default to zero in Cubic and BIC."
    > is not very safe.
    >
    > With this patch, ftp-transfer stops in my system.
    > (vsftpd-2.0.5-8)
    >
    > Please revert this patch.
    >
    >
    > Best Regards
    > Komuro
    >
    > >commit 66e1e3b20cbbf99da63e6c1af0fc6d39c2ed099a
    > >Author: David S. Miller <davem@sunset.davemloft.net>
    > >Date: Wed Jun 13 01:03:53 2007 -0700
    > >
    > > [TCP]: Set initial_ssthresh default to zero in Cubic and BIC.
    > >
    > > Because of the current default of 100, Cubic and BIC perform very
    > > poorly compared to standard Reno.
    > >
    > > In the worst case, this change makes Cubic and BIC as aggressive as
    > > Reno. So this change should be very safe.
    > >
    > > Signed-off-by: David S. Miller <davem@davemloft.net>
    > >
    > >diff --git a/net/ipv4/tcp_bic.c b/net/ipv4/tcp_bic.c
    > >index 281c9f9..dd9ef65 100644
    > >--- a/net/ipv4/tcp_bic.c
    > >+++ b/net/ipv4/tcp_bic.c
    > >@@ -29,7 +29,7 @@ static int fast_convergence = 1;
    > > static int max_increment = 16;
    > > static int low_window = 14;
    > > static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
    > >-static int initial_ssthresh = 100;
    > >+static int initial_ssthresh;
    > > static int smooth_part = 20;
    > >
    > > module_param(fast_convergence, int, 0644);
    > >diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
    > >index 1422448..ebfaac2 100644
    > >--- a/net/ipv4/tcp_cubic.c
    > >+++ b/net/ipv4/tcp_cubic.c
    > >@@ -29,7 +29,7 @@
    > > static int fast_convergence __read_mostly = 1;
    > > static int max_increment __read_mostly = 16;
    > > static int beta __read_mostly = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
    > >-static int initial_ssthresh __read_mostly = 100;
    > >+static int initial_ssthresh __read_mostly;
    > > static int bic_scale __read_mostly = 41;
    > > static int tcp_friendliness __read_mostly = 1;
    > >


    --
    Komuro <komurojun@nifty.com>
    -
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