netdev - Re: [PATCH] net: Check skb->rxhash in gro

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Message-ID: <1389332287.31367.88.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 09 Jan 2014 21:38:07 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH] net: Check skb->rxhash in gro_receive

On Thu, 2014-01-09 at 20:54 -0800, Tom Herbert wrote:
> When initializing a gro_list for a packet, first check the rxhash of
> the incoming skb against that of the skb's in the list. This should be
> a very strong inidicator of whether the flow is going to be matched,
> and potentially allows a lot of other checks to be short circuited.
> 

Hmm... this idea was discussed in the past. I used it when attempting to
use a hash table instead of a gro_list last year.

Unfortunately this added lot of cycles when rxhash is not provided by
hardware, and my tests found it was not a win.

Remember : in most cases, gro_list contains one flow, so this test does
nothing special but adds overhead.



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