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

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Message-ID: <1389332635.31367.91.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 09 Jan 2014 21:43:55 -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 21:38 -0800, Eric Dumazet wrote:

> 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.

Additional point : For napi_gro_frag() users, skb->head do not contains
headers, so flow dissector enters slow path to fetch the headers from
the fragment, one by one.



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