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

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Message-ID: <CA+mtBx-OHxHCTQO50F9_aw=T8VSg93E2eCkzdLL3PZapcR-CFQ@mail.gmail.com>
Date:	Fri, 10 Jan 2014 11:42:12 -0800
From:	Tom Herbert <therbert@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: Check skb->rxhash in gro_receive

> Really, 99% of the time gro_list contains zero or one single slot, I
> have hard data saying so.
>
Please provide the data.

> If you want to optimize the case where list is fully populated (because
> of yet another synthetic benchmark you use), you really need to build a
> temporary list so that all layers do not even have to check
> NAPI_GRO_CB(p)->same_flow
>
Well if you prefer, you can think of the "synthetic benchmark" as
emulating an obvious DOS attack by pumping MSS sized TCP segments with
random ports to a server. The stack needs to be resilient to such
things, an O(n*m) algorithm in the data path is a red flag.

> Each gro handler would remove non matching flow from this temp list.
>
> -> when we finally reach tcp_gro_receive(), list would contain a single
> element.
>
>
>
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