netdev - Re: [PATCH next-next-2.6] netdev: better dev_name

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Date:	Mon, 26 Oct 2009 16:31:44 +0200
From:	Octavian Purdila <opurdila@...acom.com>
To:	Krishna Kumar2 <krkumar2@...ibm.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Hagen Paul Pfeifer <hagen@...u.net>, netdev@...r.kernel.org
Subject: Re: [PATCH next-next-2.6] netdev: better dev_name_hash

On Monday 26 October 2009 15:07:31 you wrote:
> Eric Dumazet wrote on 10/26/2009 10:58:34 AM:
> > In fact, new10 should be the 'perfect' hash for the "eth%d"
> > netdev use, not jhash (way more expensive in cpu cycles BTW)
> >
> > Most linux machines in the world have less than 10 interfaces, jhash
> > would be really overkill.
> >
> >
> > Thanks
> >
> >
> > [PATCH net-next-2.6] netdev: better dev_name_hash
> 
> Changing Eric's test program to pass a multiplier to string_hash()
> and calling string_hash with multipler=<2 - 63> confirms that 10
> is almost always the best number for varying netdev names. I print
> the number of times perfect 64 was scored, and for most passed
> device names, the best is for n=10, followed by n=5 and others.
> Almost the worst was n=31, slightly better was n=17.
> 
> But other variables matter too, like fewer entries (4K or 1K) but
> above values for are still better compared to n=31.
> 

Hmm, I've found out that it very much depends on the name as well:

0 - orig, 1 - jhash, 2 - new10, 3 - new17, 4 - new31

$ ./dev_name_hash ixint 16000 0 16
score 24741
$ ./dev_name_hash ixint 16000 1 16
score 17949
$ ./dev_name_hash ixint 16000 2 16
score 16000
$ ./dev_name_hash ixint 16000 3 16
score 16715
$ ./dev_name_hash ixint 16000 4 16
score 18125


$ ./dev_name_hash ixunc 16000 0 16
score 24741
$ ./dev_name_hash ixunc 16000 1 16
score 17904
$ ./dev_name_hash ixunc 16000 2 16
score 22180
$ ./dev_name_hash ixunc 16000 3 16
score 17065
$ ./dev_name_hash ixunc 16000 4 16
score 18038
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