From owner-freebsd-net@freebsd.org Wed Oct 24 15:07:07 2018 Return-Path: Delivered-To: freebsd-net@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 22809FEE037 for ; Wed, 24 Oct 2018 15:07:07 +0000 (UTC) (envelope-from lev@FreeBSD.org) Received: from onlyone.not-for.work (onlyone.not-for.work [148.251.9.81]) by mx1.freebsd.org (Postfix) with ESMTP id A77B99711C for ; Wed, 24 Oct 2018 15:07:06 +0000 (UTC) (envelope-from lev@FreeBSD.org) Received: from [192.168.23.186] (unknown [89.113.128.32]) (Authenticated sender: lev@serebryakov.spb.ru) by onlyone.not-for.work (Postfix) with ESMTPSA id AE5F0DD1 for ; Wed, 24 Oct 2018 18:06:59 +0300 (MSK) To: freebsd-net@freebsd.org Reply-To: lev@FreeBSD.org From: Lev Serebryakov Subject: Very high lock contention in tcp_usr_send() which looks to limit if_gif performance with standard MTU Openpgp: preference=signencrypt Autocrypt: addr=lev@FreeBSD.org; 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WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="LPSH1QUfrB0Vb7nNGnUCTBKrbYxLyGVEh" X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 24 Oct 2018 15:07:07 -0000 This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --LPSH1QUfrB0Vb7nNGnUCTBKrbYxLyGVEh Content-Type: multipart/mixed; boundary="3qQE843I85WSOce41UXqygxSapGYHyerT"; protected-headers="v1" From: Lev Serebryakov Reply-To: lev@FreeBSD.org To: freebsd-net@freebsd.org Message-ID: <1ba8044b-9dea-8d22-1fc8-e15ff7b18794@FreeBSD.org> Subject: Very high lock contention in tcp_usr_send() which looks to limit if_gif performance with standard MTU --3qQE843I85WSOce41UXqygxSapGYHyerT Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable I've benchmarked if_gre and if_gif encapsulation on not-so-powerful hardware. Test is very simple: single as-fast-as-possible TCP stream via tunnel to much-more performant server over 1G physical interface. I was surprised by very high price of encapsulation with standard MTU of 1280 bytes. Performance in such configuration is about 45% of line speed (440Mbit instead of 1Gbit). I can not believe, that adding one header to each packet is SO expensive. Also, in such case userland thread of benchmark (nuttcp or iperf3) consumes 100% of CPU (one core) and kernel thread (if_config_tqg_0 or if_config_tqg_1) consumes 100% of CPY (second core). Physical interface with MTU of 1280 and switched off hardware "helpers" shows 800Mbit/s and CPU is not-so-consumed, userland and kernel consume about 50% + 50% of CPU, not 100% + 100%, which looks reasonable. I've traced down half of problem: userland CPU consumption to lock contention at "sys/netinet/tcp_usrreq.c:923": inp =3D sotoinpcb(so); KASSERT(inp !=3D NULL, ("tcp_usr_send: inp =3D=3D NULL")); ********INP_WLOCK(inp);******** if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) { This line consumes 75% of all time consumed by sosend(), and, effectively, by userland, via this call chain: kernel`sosend+0x79 kernel`soo_write+0x6b kernel`fo_write+0x4a kernel`dofilewrite+0xcd kernel`kern_writev+0x79 kernel`sys_write+0x8f 75% of one core is consumed by this line. Unfortunately, other party of this contention is not so obvious. Flame graph without TCO could be found here: http://lev.serebryakov.spb.ru/_sklad/gif-stacks/no-tco/gif.1280.nuttcp.s= end.no-tco.svg It looks very suspicious to me. BTW, if_gre has exactly same problem. --=20 // Lev Serebryakov --3qQE843I85WSOce41UXqygxSapGYHyerT-- --LPSH1QUfrB0Vb7nNGnUCTBKrbYxLyGVEh Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQKTBAEBCgB9FiEE+W0coLX0MYtnSzMK6rA8WL/cR48FAlvQio1fFIAAAAAALgAo aXNzdWVyLWZwckBub3RhdGlvbnMub3BlbnBncC5maWZ0aGhvcnNlbWFuLm5ldEY5 NkQxQ0EwQjVGNDMxOEI2NzRCMzMwQUVBQjAzQzU4QkZEQzQ3OEYACgkQ6rA8WL/c R49tEA/+JWDnBoNhcxpEWSzxW8iuvJUScaomO1Vm/rBAI9W1Ty3FKMpm2deQiQqB RuAGKJFvEtFiJrTKhox55Cs13n0tAP/+epLqr3up7j9y8Yek9hFGPIz8Vg6Cqv0W fXSqqjrdg0fHZO7dYNGYNWTv9pFhgYYr+ArqIGwRW1L99n1PnjLXwDMKfqODrpDS WUSEHcjDDK1JVV69KFRkaFFpCUI8usaHleymXSBem4MhvU0LZQdIkU8Elf6AIQAE qJ4wyiyn2hv6ZrDuqzEEdF1AvbKClKnvGJxfLYos1U7yCFHkKLgLEfS4bx1HdQ9C D9iyRzGSLB1eTdWModOIugzrUgYcYZMOmKbhGMqiyOi+POjH68BQY36q4K8JEd4X 4RIqHuV2uENLWgVASDyIFXqEIVPzu8R/P44ajJxOsrfsSIW4WNrSoEmsgt9SSUmR /JGN4FxZfIJ5MJ/IyfcZjBSCBW6uDN/LsdhME9GyytkEONiCC3L8PEk8Gok2sgQp kIWhnpteS2QCIhE7jLt/bvhpi40TMBJaOj1oq7GZnD4w8C1eE0CvGNWkBb52UJDW Xb4kT4XXyCXUPMfxH3T25XS5Wo/H+XrhsdJa1/MRqS0pxBT7F6va9b6WaCsaftyU 9mN6mQp4Z4V8mNh6JQzZgIi95LYAIou4bCqbad3ugk8T+69a0pg= =KcLL -----END PGP SIGNATURE----- --LPSH1QUfrB0Vb7nNGnUCTBKrbYxLyGVEh--