netdev - Re: [PATCH net-next v6] rps: selective flow shedding during softnet overflow

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Date:	Mon, 20 May 2013 09:00:54 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Willem de Bruijn <willemb@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v6] rps: selective flow shedding during softnet
 overflow

On Mon, 2013-05-20 at 10:02 -0400, Willem de Bruijn wrote:
> A cpu executing the network receive path sheds packets when its input
> queue grows to netdev_max_backlog. A single high rate flow (such as a
> spoofed source DoS) can exceed a single cpu processing rate and will
> degrade throughput of other flows hashed onto the same cpu.
> 
> This patch adds a more fine grained hashtable. If the netdev backlog
> is above a threshold, IRQ cpus track the ratio of total traffic of
> each flow (using 4096 buckets, configurable). The ratio is measured
> by counting the number of packets per flow over the last 256 packets
> from the source cpu. Any flow that occupies a large fraction of this
> (set at 50%) will see packet drop while above the threshold.
> 
> Tested:
> Setup is a muli-threaded UDP echo server with network rx IRQ on cpu0,
> kernel receive (RPS) on cpu0 and application threads on cpus 2--7
> each handling 20k req/s. Throughput halves when hit with a 400 kpps
> antagonist storm. With this patch applied, antagonist overload is
> dropped and the server processes its complete load.
> 
> The patch is effective when kernel receive processing is the
> bottleneck. The above RPS scenario is a extreme, but the same is
> reached with RFS and sufficient kernel processing (iptables, packet
> socket tap, ..).
> 
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> 
> ---

Acked-by: Eric Dumazet <edumazet@...gle.com>

Willemb, are you planning to add a section in
Documentation/networking/scaling.txt ?

Thanks


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