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From: Florian Westphal <fw@strlen.de>
To: Tom Herbert <therbert@google.com>
Cc: Florian Westphal <fw@strlen.de>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	David Miller <davem@davemloft.net>,
	Linux Netdev List <netdev@vger.kernel.org>
Subject: Re: [PATCH net-next 3/6] flow_dissector: Add hash_extra field to flow_keys struct
Date: Sun, 1 Mar 2015 20:43:48 +0100	[thread overview]
Message-ID: <20150301194348.GB23622@breakpoint.cc> (raw)
In-Reply-To: <CA+mtBx_9SKncJ1hfKj9icJP8bFbSKrHijeJoFOm7dU5MdwejRg@mail.gmail.com>

Tom Herbert <therbert@google.com> wrote:
> We still need hash perturbation for the mapping to a small number of
> queues which can be done after retrieving skb_get_hash, but the
> probability that two different flows match perfectly in skb_get_hash()
> should be 1/2^32-- so are hash collisions really a concern here?

I'm not concerned about accidental collisions, how predictable is skb_get_hash()?
Is skb_get_hash() guaranteed to e.g. contain L4 information?

AFAIK answer to both is "depends on nic/driver", so I feel its better to use
software flow dissector.

  reply	other threads:[~2015-03-01 19:43 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-28  3:11 [PATCH net-next 0/6] net: Strengthen TX and RX hashes Tom Herbert
2015-02-28  3:11 ` [PATCH net-next 1/6] net: initialize sk_txhash using random value Tom Herbert
2015-02-28  3:11 ` [PATCH net-next 2/6] flow_dissector: Include ip_proto in hash computation Tom Herbert
2015-02-28  3:11 ` [PATCH net-next 3/6] flow_dissector: Add hash_extra field to flow_keys struct Tom Herbert
2015-02-28  7:37   ` Eric Dumazet
2015-02-28 20:31     ` Florian Westphal
2015-02-28 20:46       ` Dave Taht
2015-03-01 18:16         ` Tom Herbert
2015-03-01 20:09           ` Dave Taht
2015-03-01 17:55       ` Tom Herbert
2015-03-01 18:24         ` Florian Westphal
2015-03-01 19:17           ` Tom Herbert
2015-03-01 19:43             ` Florian Westphal [this message]
2015-03-01 19:57           ` Dave Taht
2015-03-01 21:27         ` Eric Dumazet
2015-02-28  3:11 ` [PATCH net-next 4/6] flow_dissector: Include VLAN ID in hash computation Tom Herbert
2015-02-28  3:11 ` [PATCH net-next 5/6] flow_dissector: Include GRE keyid " Tom Herbert
2015-02-28  3:11 ` [PATCH net-next 6/6] flow_dissector: Include MPLS entropy label " Tom Herbert

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