On 04/19/2017 10:13 PM, Eric Dumazet wrote: > On Wed, 2017-04-19 at 20:48 +0200, Michael Kerrisk (man-pages) wrote: >> Hi Eric, >> >> [reodering for clarity] >> >>>> 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. >> >>> Hi Michael >>> >>> Sorry for the delay. >> >> Thanks for the reply, but I think you are assuming I know more than >> I do. I'd like you to elaborate a little please. See below. >> >>> Note that setting the option is not supported if SO_REUSEPORT is used. >> >> Please define "not supported". Does this yield an API diagnostic? >> If so, what is it? >> >>> Socket will be selected from an array, either by a hash or BPF program >>> that has no access to this information. >> >> Sorry -- I'm lost here. How does this comment relate to the proposed >> man page text above? > > Simply that : > > If an application uses both SO_INCOMING_CPU and SO_REUSEPORT, then > SO_REUSEPORT logic, selecting the socket to receive the packet, ignores > SO_INCOMING_CPU setting. > > This does not need to be documented, because it is an implementation > detail/bug that could be changed, if someone cares enough. Okay, thanks, Eric. I'll just merge the page text as it currently is then. 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@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
