netdev - RE: [PATCH net-next 0/6] net: Call skb_get

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CAF571E@AcuExch.aculab.com>
Date:	Thu, 5 Mar 2015 11:13:35 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Tom Herbert' <therbert@...gle.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	"fw@...len.de" <fw@...len.de>
Subject: RE: [PATCH net-next 0/6] net: Call skb_get_hash in qdiscs

From: Tom Herbert
...
> - The probability that two different flows randomly match to the same
>   hash from skb_get_hash is 1/2^32. If such a collision were to happen,
>   then the flows potentially also map to the same qdisc queue in
>   perpetuity despite perturbation being performed. Given the very low
>   probability of this occurring, this may in practice only be an
>   academic issue. If it is a real concern, rekeying of the underlying
>   mechanisms of skb->hash could be done.
...

The probability of a collision is much higher than that.
With 10000 flows it is (if my 'ballpark maths' is right) nearer 1/100.

	David

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