netdev - Re: [PATCH RFC]: soreuseport: Bind multiple sockets to same port

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Date:	Mon, 19 Apr 2010 08:31:41 -0400
From:	jamal <hadi@...erus.ca>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Tom Herbert <therbert@...gle.com>, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH RFC]: soreuseport: Bind multiple sockets to same port

On Mon, 2010-04-19 at 09:28 +0200, Eric Dumazet wrote:

> High perf DNS server on such machine would have 16 threads, and probably
> 64 threads in two years.

if you dont care about x86, 64 SMT threads is already there
yesterday ;->

> I understand you want 16 UDP sockets to avoid lock contention, but
> __udp4_lib_lookup() becomes a nightmare (It may already be ...)
> 
> My idea was to add a cpu lookup key.

I like this idea better. 
Staring at data i collected over the weekend, I am scratching my head
trying to find some correlation. I see socket flows  bouncing around
CPUs other than what RPS directs to. The scheduler seems to have a mind
of its own. What is clear is if i can localize a flow/socket to a single
cpu i get best performance. RPS, when there is enough load, does better
because of this localization (DaveM made this statement earlier
actually).

I was hoping i could do a connect() + sched_setaffinity() and have RPS
direct that flow to me - but alas even RFS still depends on hashing.
Unless there is an easier way to do this, I was planning to look
at the RPS hashing and manually cook flows which end up on a cpu where 
I do sched_setaffinity()...

> thread0 would use a new setsockopt() option to bind a socket to a
> virtual cpu0. Then do its normal bind( port=53)

So question: Why not tie to sched_setaffinity? i.e at bind time you
lookup what cpu this socket is affined to?

cheers,
jamal

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