linux-kernel - [NOT VERY SAFE] [TCP]: Set initial_ssthresh default to zero in Cubic and BIC.

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Message-Id: <20071014073658.d4352b8c.komurojun@nifty.com>
Date:	Sun, 14 Oct 2007 07:36:58 +0900
From:	Komuro <komurojun@...ty.com>
To:	davem@...set.davemloft.net
Cc:	linux-kernel@...r.kernel.org
Subject: [NOT VERY SAFE]     [TCP]: Set initial_ssthresh default to zero in
 Cubic and BIC.


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@...set.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@...emloft.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;
> 
-
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