From mboxrd@z Thu Jan 1 00:00:00 1970 From: Norbert van Bolhuis Subject: Re: single process receives own frames due to PACKET_MMAP Date: Tue, 07 Jan 2014 16:46:48 +0100 Message-ID: <52CC2168.9060401@aimvalley.nl> References: <52B4465E.2090904@aimvalley.nl> <52CB34F9.6020906@aimvalley.nl> <52CBC991.8030701@redhat.com> <20140107110609.74f71979@redhat.com> <52CBFE13.8@aimvalley.nl> <20140107150938.1058b358@redhat.com> <52CC1A61.5080205@aimvalley.nl> <52CC1C94.2060808@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Jesper Dangaard Brouer , netdev@vger.kernel.org, David Miller , uaca@alumni.uv.es To: Daniel Borkmann Return-path: Received: from mika.eatserver.nl ([195.20.9.75]:51879 "EHLO mika.eatserver.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752937AbaAGPsA (ORCPT ); Tue, 7 Jan 2014 10:48:00 -0500 In-Reply-To: <52CC1C94.2060808@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On 01/07/14 16:26, Daniel Borkmann wrote: > On 01/07/2014 04:16 PM, Norbert van Bolhuis wrote: >> On 01/07/14 15:09, Jesper Dangaard Brouer wrote: >>> On Tue, 07 Jan 2014 14:16:03 +0100 >>> Norbert van Bolhuis wrote: >>>> On 01/07/14 11:06, Jesper Dangaard Brouer wrote: >>>>> On Tue, 07 Jan 2014 10:32:01 +0100 >>>>> Daniel Borkmann wrote: >>>>> >>>>>> On 01/06/2014 11:58 PM, Norbert van Bolhuis wrote: >>>>>>> >>> [...] >>>>>> >>>>>>> I'd say it makes no sense to make the same process receive its >>>>>>> own transmitted frames on that same interface (unless its lo). >>>>> >>>>> Have you setup: >>>>> ring->s_ll.sll_protocol = 0 >>>>> >>>>> This is what I did in trafgen to avoid this problem. >>>>> >>>>> See line 55 in netsniff-ng/ring.c: >>>>> https://github.com/borkmann/netsniff-ng/blob/c3602a995b21e8133c7f4fd1fb1e7e21b6a844f1/ring.c#L55 >>>>> >>>>> Commit: >>>>> https://github.com/borkmann/netsniff-ng/commit/c3602a995b21e8133c7f4fd1fb1e7e21b6a844f1 >>>>> >>>> >>>> >>>> No I did not do that, I was checking my code against netsniff-ng-0.5.8-rc4. >>>> >>>> But I just tried it, I believe I do the same as netsniff-ng-0.5.8-rc5, but it doesn't >>>> work for me. Maybe because I have an old FC14 system (kernel 2.6.35.14-106.fc14.x86_64). >>>> >>>> So I tried to see whether netsniff-ng-0.5.8-rc5/trafgen still makes the >>>> kernel call packet_rcv() on my FC14 system. So I build and run it, but I'm not sure >>>> how to (easily) check that. >>> >>> The easiest way is to: >>> cat /proc/net/ptype >>> And look if someone registered a proto handler/function: packet_rcv (or tpacket_rcv). >>> >>> The more exact method is, to run "perf record -a -g" and then look (at >>> the result with "perf report") for a lock contention, and "expand" the >>> spin_lock and see if packet_rcv() is calling this spin lock. >>> >> >> >> I checked the easy way. >> Even on my old FC14 system the "protocol=0 patch" seems to make a difference >> for trafgen. >> Without the patch I see for each CPU in use by trafgen a "packet_rcv entry" in >> /proc/net/ptype. >> With the patch I see no additional "packet_rcv entry". > > Yes, that is expected behaviour. ;-) See more below. > >> It could be my Appl is wrong or maybe the "protocol=0 patch" does not help. >> I think the latter, afterall my Appl has, unlike trafgen, another RX >> (AF_PACKET) socket. >> >> >>> >>>> In anyway, Wireshark does capture the trafgen generated >>>> frames, does that say anything ? >>> >>> Be careful not to start a wireshark/tcpdump, at the sametime, as this >>> will slow you down. >>> >>>> In the future, I can at least use PACKET_QDISC_BYPASS as a "workaround". >>> >>> And in the future with PACKET_QDISC_BYPASS, your wireshark will not >>> catch these packets, remember that. >>> >> >> >> Yes, this is why I would love to see the "protocol=0 patch" work for my Appl. >> >> So I will try my Appl with the latest net-next kernel to see if that makes >> it work. Hopefully I can find some time in the next coming days, I will keep >> you informed. > > As long as there's at least one single PF_PACKET receive socket open and you > do not make use of PACKET_QDISC_BYPASS on your tx socket, then those packets go > back the dev_queue_xmit_nit() path, even if your tx socket uses protocol=0. > > If you make use of PACKET_QDISC_BYPASS [1] for your particular tx socket, then > packets generated by that socket will not hit the dev_queue_xmit_nit() path > back to other possible rx listeners that are present on your system (w/ the > side-effects for tx as described in [1]). > > [1] Documentation/networking/packet_mmap.txt +960 > Ok, that's clear. But this means my PF_PACKET socket application performs worse because of using PACKET_MMAP. I expected the opposit. Afterall my old PF_PACKET socket application (which does not use PACKET_MMAP) uses only one PF_PACKET socket (for TX and RX). Because packets are never sent back to the socket they originated from, my old PF_PACKET socket application performs better. Is there a way to use one PF_PACKET socket for both TX and RX and use PACKET_MMAP ? --- Norbert