netdev - Re: UDP multi-core performance on a single socket and SO

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Date:	Fri, 04 Jan 2013 11:37:18 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Mark Zealey <netdev@...kandruth.co.uk>
Cc:	netdev@...r.kernel.org
Subject: Re: UDP multi-core performance on a single socket and SO_REUSEPORT

On Fri, 2013-01-04 at 18:50 +0000, Mark Zealey wrote:
> I have written two small test scripts now which can be found at 
> http://mark.zealey.org/uploads/ - one launches 16 listening threads for 
> a single UDP socket, the other needs to be run as
> 
> for i in `seq 16`; do ./udp_test_client & done
> 
> On my test server (32-core), stock kernel 3.7.1, 90% of the time is 
> spent in the kernel waiting on spinlocks. Perf output:

Mark

We know the scalability issue of using a single socket and many threads.

The send path was somehow fixed to not require socket lock.

But the receive path uses a single receive_queue, protected by a
spinlock.

SO_REUSEPORT would be nice, but had known issues.

af_packet fanout implementation was nicer.
You could try :

1) Use af_packet FANOUT instead of UDP sockets

2) rewrite SO_REUSEPORT to use a FANOUT like implementation

3) Extend UDP sockets to be able to use a configurable number of receive
queues instead of a single one.



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