From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael Kerrisk (man-pages)" Subject: Re: [patch] socket.7: Document SO_INCOMING_CPU Date: Sun, 19 Feb 2017 21:55:20 +0100 Message-ID: <63815aac-9c8f-c599-9422-5c312cefc9e8@gmail.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Eric Dumazet To: Francois Saint-Jacques Return-path: In-Reply-To: Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: netdev.vger.kernel.org [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/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html