netdev - Re: [PATCH net-next] net: introduce SO_INCOMING

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Date:	Fri, 14 Nov 2014 15:03:44 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Tom Herbert <therbert@...gle.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Ying Cai <ycai@...gle.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH net-next] net: introduce SO_INCOMING_CPU

On Fri, Nov 14, 2014 at 2:58 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2014-11-14 at 14:27 -0800, Andy Lutomirski wrote:
>
>> The people at the other end will be really pissed if that results in
>> lots of reconnections.
>
> No reconnections necessary.
>
> I believe you misunderstood : On the 4-tuple (SADDR,SPORT,DADDR,DPORT),
> you can pick for example SPORT so that hash(SADDR,SPORT,DADDR,DPORT)
> maps to a known and wanted RX queue number.
>
> Once you know that, you use bind(SADDR, SPORT), then
> connect(DADDR,DPORT).

If the kernel had an API for this, I'd be all for using it.

>
> Anyway, if your hardware is able to cope with the few number of flows,
> just use the hardware and be happy.
>
> Here we want about 10 millions sockets, there is little hope for
> hardware being helpful.
>

It's the intermediate numbers that are bad.

With ten flows, the current accelerated RFS works fine.  With 10M
flows, RFS is a lost cause and this solution is much nicer.  With,
say, 1k flows, accelerated RFS *deserves* to work perfectly, because
the hardware has enough filter slots.  But making it work reliably
requires a ridiculously large hash table, and collisions cause silent
bad behavior.

--Andy

>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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