netdev - Re: [PATCH 1/1] net: Add SO_REUSEPORT_LISTEN

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Date:	Fri, 25 Mar 2016 06:17:24 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yann Ylavic <ylavic.dev@...il.com>
Cc:	Willy Tarreau <w@....eu>, Tom Herbert <tom@...bertland.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Tolga Ceylan <tolga.ceylan@...il.com>,
	Craig Gallek <cgallek@...gle.com>,
	Josh Snyder <josh@...e406.com>,
	Aaron Conole <aconole@...heb.org>,
	"David S. Miller" <davem@...emloft.net>,
	Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH 1/1] net: Add SO_REUSEPORT_LISTEN_OFF socket option as
 drain mode

On Fri, 2016-03-25 at 12:21 +0100, Yann Ylavic wrote:

> Not my intention, you guys know what's the better for the kernel and its APIs.
> My concern is (was) admittedly due to my own lack of knowledge of
> (e)BPF, hence how much of kernel internals I'd need to know to make
> the SO_REUSEPORT work in my case.
> 
> But sure, any of the help suggested above would make it go away, I'll
> stay tuned.

Most of the time, the BPF filter can be trivial.

If your server has a multi queue NIC with 16 queues on a 16 cpus host,
it would be natural to use 16 listeners, to properly use the NIC
features (RSS).

BPF program would be

A = QUEUE_NUMBER(skb);
RETURN A;

If you chose to have 4 listeners instead, for whatever reasons.

A = QUEUE_NUMBER(skb);
A = A & 3;
RETURN A;


You also can use 

A = CURRENT_CPU;
RETURN A;