netdev - Re: [patch] socket.7: Document SO_INCOMING

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Message-ID: <9c754f31-8ace-03f2-97f3-81e29eb6d997@gmail.com>
Date:   Wed, 19 Apr 2017 15:20:31 +0200
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Francois Saint-Jacques <fsaintjacques@...il.com>
Cc:     mtk.manpages@...il.com, linux-man@...r.kernel.org,
        netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>
Subject: Re: [patch] socket.7: Document SO_INCOMING_CPU

Ping Eric!

Would you have a chance to review the proposed text below, please.

Thanks,

Michael

On 02/19/2017 09:55 PM, Michael Kerrisk (man-pages) wrote:
> [CC += Eric, so that he might review]
> 
> Hello Francois,
> 
> On 02/18/2017 05:06 AM, Francois Saint-Jacques wrote:
>> This socket option is undocumented. Applies on the latest version
>> (man-pages-4.09-511).
>>
>> diff --git a/man7/socket.7 b/man7/socket.7
>> index 3efd7a5d8..1a3ffa253 100644
>> --- a/man7/socket.7
>> +++ b/man7/socket.7
>> @@ -490,6 +490,26 @@ flag on a socket
>>  operation.
>>  Expects an integer boolean flag.
>>  .TP
>> +.BR SO_INCOMING_CPU " (getsockopt since Linux 3.19, setsockopt since
>> Linux 4.4)"
>> +.\" getsocktop 2c8c56e15df3d4c2af3d656e44feb18789f75837
>> +.\" setsocktop 70da268b569d32a9fddeea85dc18043de9d89f89
>> +Sets or gets the cpu affinity of a socket. Expects an integer flag.
>> +.sp
>> +.in +4n
>> +.nf
>> +int cpu = 1;
>> +socklen_t len = sizeof(cpu);
>> +setsockopt(fd, SOL_SOCKET, SO_INCOMING_CPU, &cpu, &len);
>> +.fi
>> +.in
>> +.sp
>> +The typical use case is one listener per RX queue, as the associated listener
>> +should only accept flows handled in softirq by the same cpu.  This provides
>> +optimal NUMA behavior and keep cpu caches hot.
>> +.TP
>>  .B SO_KEEPALIVE
>>  Enable sending of keep-alive messages on connection-oriented sockets.
>>  Expects an integer boolean flag.
> 
> Thank you! Patch applied.
> 
> I have tried to enhance the description somewhat. I'm not sure whether
> what I've written is quite correct (or whether it should be further
> extended). Eric, could you please take a look at the following, and let 
> me know if anything needs fixing:
> 
>        SO_INCOMING_CPU  (gettable  since Linux 3.19, settable since Linux
>        4.4)
>               Sets or gets the CPU affinity  of  a  socket.   Expects  an
>               integer flag.
> 
>                   int cpu = 1;
>                   socklen_t len = sizeof(cpu);
>                   setsockopt(fd, SOL_SOCKET, SO_INCOMING_CPU, &cpu, &len);
> 
>               Because  all  of the packets for a single stream (i.e., all
>               packets for the same 4-tuple) arrive on the single RX queue
>               that  is  associated with a particular CPU, the typical use
>               case is to employ one listening process per RX queue,  with
>               the  incoming  flow being handled by a listener on the same
>               CPU that is handling the RX queue.  This  provides  optimal
>               NUMA behavior and keeps CPU caches hot.
> 
> Cheers,
> 
> Michael
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/