linux-kernel - Re: 2.6.21 -> 2.6.22 & 2.6.23-rc8 performance regression

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Message-Id: <20071001.135710.99174896.davem@davemloft.net>
Date:	Mon, 01 Oct 2007 13:57:10 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	dada1@...mosbay.com
Cc:	nuclearcat@...learcat.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: 2.6.21 -> 2.6.22 & 2.6.23-rc8 performance regression

From: Eric Dumazet <dada1@...mosbay.com>
Date: Mon, 01 Oct 2007 22:10:03 +0200

> So maybe the following patch is necessary...
> 
> I believe IPV6 & DCCP are immune to this problem.
> 
> Thanks again Denys for spotting this.
> 
> Eric
> 
> [PATCH] TCP : secure_tcp_sequence_number() should not use a too fast clock
> 
> TCP V4 sequence numbers are 32bits, and RFC 793 assumed a 250 KHz clock.
> In order to follow network speed increase, we can use a faster clock, but
> we should limit this clock so that the delay between two rollovers is
> greater than MSL (TCP Maximum Segment Lifetime : 2 minutes)
> 
> Choosing a 64 nsec clock should be OK, since the rollovers occur every
> 274 seconds.
> 
> Problem spotted by Denys Fedoryshchenko
> 
> Signed-off-by: Eric Dumazet <dada1@...mosbay.com>

Thanks a lot Eric for bringing closure to this.

I'll apply this and add a reference in the commit message to the
changeset that introduced this problem, since it might help
others who look at this.
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