Re: [patch] socket.7: Document SO_INCOMING_CPU
From: Michael Kerrisk (man-pages) <hidden>
Date: 2017-02-19 20:55:20
Also in:
netdev
[CC += Eric, so that he might review] Hello Francois, On 02/18/2017 05:06 AM, Francois Saint-Jacques wrote:
quoted hunk
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 sinceLinux 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/
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