netdev - Re: [PATCH 1/2 v2] net: Add function to get SW rxhash

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Message-ID: <1380058203.3165.121.camel@edumazet-glaptop>
Date:	Tue, 24 Sep 2013 14:30:03 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2 v2] net: Add function to get SW rxhash

On Tue, 2013-09-24 at 13:42 -0700, Tom Herbert wrote:
> Some uses of skb_get_rxhash expect that the function will return
> a consistent value whether it is called on RX or TX paths. On RX
> path, we will use the rxhash if provided by the NIC, so this
> would not normally be the same result computed in TX path would be
> a software calculation.
> 
> This patch adds skb_get_sw_rxhash to explicitly request a hash
> calculated by the stack, disregarding the hash provided by NIC.

As I said, I think this is overhead in network fast path.

This can be done without adding a new skb field.

I suspect tun should not use rxhash but a proper hash, as conntrack or
tcp...



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