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From: Komuro <komurojun@nifty.com>
To: davem@sunset.davemloft.net
Cc: linux-kernel@vger.kernel.org
Subject: Re: [NOT VERY SAFE]     [TCP]: Set initial_ssthresh default to zero in Cubic and BIC.
Date: Sun, 14 Oct 2007 10:02:45 +0900	[thread overview]
Message-ID: <20071014100245.914b784a.komurojun@nifty.com> (raw)
In-Reply-To: <20071014073658.d4352b8c.komurojun@nifty.com>

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>

  parent reply	other threads:[~2007-10-14  1:03 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-10-06  4:26 [PATCH] Simplify yenta code Komuro
2007-10-08 17:47 ` Linas Vepstas
2007-10-13 22:36 ` [NOT VERY SAFE] [TCP]: Set initial_ssthresh default to zero in Cubic and BIC Komuro
2007-10-13 22:52   ` David Miller
2007-10-13 22:54     ` David Miller
2007-10-14  1:02   ` Komuro [this message]
2007-10-14  2:38     ` David Miller
2007-10-14  4:30       ` Jeff Garzik
2007-10-14  4:28     ` Komuro
2007-10-14  4:32       ` David Miller
2007-10-14  4:53       ` Komuro
2007-10-14  5:23         ` David Miller
2007-10-15 12:59         ` Komuro
2007-10-15 15:55           ` Stephen Hemminger
2007-10-14 20:34     ` Stephen Hemminger
2008-03-02 12:07   ` [BUG kernel 2.6.25-rc3 IPV6] ping6 -I eth0 ff02::1 causes system hang Komuro
2008-03-04  7:40     ` Andrew Morton
2008-03-08  4:44     ` Komuro
2008-03-08  5:20       ` Komuro
2008-03-08 11:56       ` David Miller

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