netdev - Re: [PATCH net-next v2] packet: packet fanout rollover during socket overload

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Date:	Mon, 18 Mar 2013 19:16:04 -0400
From:	Willem de Bruijn <willemb@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next v2] packet: packet fanout rollover during socket overload

On Mon, Mar 18, 2013 at 7:10 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Mon, 2013-03-18 at 19:07 -0400, Willem de Bruijn wrote:
>> Minimize packet drop in a fanout group. If one socket is full,
>> roll over packets to another from the group. Maintain flow
>> affinity during normal load using an rxhash fanout policy, while
>> dispersing unexpected traffic storms that hit a single cpu, such
>> as spoofed-source DoS flows. Rollover breaks affinity for flows
>> arriving at saturated sockets during those conditions.
>>
>> The patch adds a fanout policy ROLLOVER that rotates between sockets,
>> filling each socket before moving to the next. It also adds a fanout
>> flag ROLLOVER. If passed along with any other fanout policy, the
>> primary policy is applied until the chosen socket is full. Then,
>> rollover selects another socket, to delay packet drop until the
>> entire system is saturated.
>>
>> Probing sockets is not free. Selecting the last used socket, as
>> rollover does, is a greedy approach that maximizes chance of
>> success, at the cost of extreme load imbalance. In practice, with
>> sufficiently long queues to absorb bursts, sockets are drained in
>> parallel and load balance looks uniform in `top`.
>>
>> To avoid contention, scales counters with number of sockets and
>> accesses them lockfree. Values are bounds checked to ensure
>> correctness.
>>
>> Tested using an application with 9 threads pinned to CPUs, one socket
>> per thread and sufficient busywork per packet operation to limits each
>> thread to handling 32 Kpps. When sent 500 Kpps single UDP stream
>> packets, a FANOUT_CPU setup processes 32 Kpps in total without this
>> patch, 270 Kpps with the patch. Tested with read() and with a packet
>> ring (V1).
>>
>> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
>> ---
>
> Reviewed-by: Eric Dumazet <edumazet@...gle.com>

Thanks Eric.

I need to rebase the patch once more to have it apply cleanly.

>
>
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