From: "Brian F. G. Bidulock" <bidulock@openss7.org>
To: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Cc: David Miller <davem@davemloft.net>,
draghuram@rocketmail.com, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org
Subject: Re: Question about tcp hash function tcp_hashfn()
Date: Wed, 31 May 2006 03:51:24 -0600 [thread overview]
Message-ID: <20060531035124.B3065@openss7.org> (raw)
In-Reply-To: <20060531090301.GA26782@2ka.mipt.ru>; from johnpol@2ka.mipt.ru on Wed, May 31, 2006 at 01:03:02PM +0400
Evgeniy,
On Wed, 31 May 2006, Evgeniy Polyakov wrote:
> 2. Compared Jenkins hash with XOR hash used in TCP socket selection code.
> http://tservice.net.ru/~s0mbre/blog/2006/05/14#2006_05_14
Two problems with the comparison:
Port numbers can be collected into a 32 bit register in network
byte order directly from the TCP packet without taking two 16 bit
values and shifting and or'ing them.
Worse: he folded the jenkins algorith result with
h ^= h >> 16;
h ^= h >> 8;
Destroying the coverage of the function.
I, for one, am not suprised that artifacts appeared in the comparison
as a result of this destruction of the coverage of the hashing function.
next prev parent reply other threads:[~2006-05-31 9:51 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-31 4:29 Question about tcp hash function tcp_hashfn() Raghuram
2006-05-31 5:55 ` Brian F. G. Bidulock
2006-05-31 7:10 ` David Miller
2006-05-31 7:45 ` Brian F. G. Bidulock
2006-05-31 7:49 ` David Miller
2006-05-31 8:00 ` Brian F. G. Bidulock
2006-05-31 9:03 ` Evgeniy Polyakov
2006-05-31 9:12 ` David Miller
2006-05-31 9:44 ` Evgeniy Polyakov
2006-05-31 9:51 ` Brian F. G. Bidulock [this message]
2006-05-31 10:58 ` Evgeniy Polyakov
2006-05-31 11:04 ` Evgeniy Polyakov
2006-05-31 13:06 ` Evgeniy Polyakov
2006-05-31 18:29 ` Brian F. G. Bidulock
2006-06-01 6:12 ` Evgeniy Polyakov
2006-06-01 6:18 ` David Miller
2006-06-01 6:22 ` Brian F. G. Bidulock
2006-06-01 6:24 ` David Miller
2006-05-31 18:41 ` David Miller
2006-06-01 6:04 ` Evgeniy Polyakov
2006-06-01 6:18 ` Brian F. G. Bidulock
2006-06-01 6:30 ` Evgeniy Polyakov
2006-06-01 6:46 ` Brian F. G. Bidulock
2006-06-01 7:01 ` Evgeniy Polyakov
2006-06-01 7:11 ` Brian F. G. Bidulock
2006-06-01 8:38 ` Evgeniy Polyakov
2006-06-01 10:24 ` Brian F. G. Bidulock
2006-06-01 11:06 ` Evgeniy Polyakov
2006-06-01 18:40 ` Brian F. G. Bidulock
2006-06-01 20:21 ` David Miller
2006-06-02 7:01 ` Evgeniy Polyakov
2006-06-02 5:40 ` Florian Weimer
2006-06-02 7:48 ` Evgeniy Polyakov
2006-06-02 15:10 ` Brian F. G. Bidulock
2006-06-02 17:26 ` Florian Weimer
2006-06-02 17:37 ` Brian F. G. Bidulock
2006-05-31 9:52 ` Brian F. G. Bidulock
2006-05-31 8:49 ` Brian F. G. Bidulock
2006-05-31 9:02 ` David Miller
2006-05-31 9:39 ` Brian F. G. Bidulock
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