netdev - Re: [PATCH 1/2] net: Toeplitz library functions

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Date:	Tue, 24 Sep 2013 10:34:35 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
Subject: Re: [PATCH 1/2] net: Toeplitz library functions

On Tue, 2013-09-24 at 10:03 -0700, Tom Herbert wrote:
> On Tue, Sep 24, 2013 at 9:46 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > On Tue, 2013-09-24 at 09:35 -0700, Tom Herbert wrote:
> >
> >> We should really be using rxhash for that anyway, eliminate this
> >> ehashfn.  This would entail adding rxhash argument in the various
> >> udp_lookup functions.
> >
> > Nope : Some NICs provide UDP rxhash only using L3  (source IP,
> > destination IP), not L4 (adding source & destination ports)
> >
> Then the NIC won't set l4_rxhash and we'll rehash over 4-tuple when
> skb_get_rxhash is called.

Yes, but then in this case you add cpu cycles for no reason.

If you have multiqueue NIC, you do not use RPS/RFS, so skb->rxhash might
be 0

hash = inet_ehashfn(net, daddr, hnum, saddr, sport);

is faster than the whole flow dissection game.





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