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

David Miller
2007-10-01T20:57:20Z

From: Eric Dumazet <dada1@cosmosbay.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@cosmosbay.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.