From owner-freebsd-stable@freebsd.org Mon Sep 19 22:59:29 2016 Return-Path: Delivered-To: freebsd-stable@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 5B27FBE1980 for ; Mon, 19 Sep 2016 22:59:29 +0000 (UTC) (envelope-from lyndon@orthanc.ca) Received: from orthanc.ca (orthanc.ca [IPv6:2607:f2f8:abf8::2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "orthanc.ca", Issuer "Let's Encrypt Authority X1" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 39F2DFA for ; Mon, 19 Sep 2016 22:59:29 +0000 (UTC) (envelope-from lyndon@orthanc.ca) Received: from [192.168.43.199] ([24.114.44.91]) (authenticated bits=0) by orthanc.ca (8.15.2/8.15.2) with ESMTPSA id u8JMxRdA056305 (version=TLSv1 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 19 Sep 2016 15:59:28 -0700 (PDT) (envelope-from lyndon@orthanc.ca) Subject: Re: LAGG and Jumbo Frames Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Content-Type: multipart/signed; boundary="Apple-Mail=_DE3568EF-F524-45B3-92F1-C07102A1522F"; protocol="application/pgp-signature"; micalg=pgp-sha256 X-Pgp-Agent: GPGMail From: Lyndon Nerenberg In-Reply-To: <20160919220812.GG2960@zxy.spb.ru> Date: Mon, 19 Sep 2016 15:59:20 -0700 Cc: FreeBSD Stable Message-Id: <42A03EA9-7F8E-446E-B430-7431AB9CE2E6@orthanc.ca> References: <48926c6013f938af832c17e4ad10b232@dweimer.net> <04c9065ee4a780c6f8986d1b204c4198@dweimer.net> <20160919220812.GG2960@zxy.spb.ru> To: Slawa Olhovchenkov X-Mailer: Apple Mail (2.3124) X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 19 Sep 2016 22:59:29 -0000 --Apple-Mail=_DE3568EF-F524-45B3-92F1-C07102A1522F Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii > On Sep 19, 2016, at 3:08 PM, Slawa Olhovchenkov = wrote: >=20 > This is because RTT of this link for jumbo frames higher 1500 bytes > frame for store-and-forward switch chain. For TCP, RTT isn't really a factor (in this scenario), as the windowing = and congestion avoidance algorithms will adapt to the actual = bandwidth-delay product of the link, and the delays in each direction = will be symmetrical. Now the ack for a single 9000 octet packet will take longer than that = for a 1500 octet one, but that's because you're sending six times as = many octets before the ACK can be generated. The time to send six 1500 = octet packets and receive the ACK from sixth packet is going to be = comparable to that of receiving the ack from a single 9000 octet packet. = It's simple arithmetic to calculate the extra protocol header overhead = for 6x1500 vs 1x9000. If there *is* a significant difference (beyond the extra protocol header = overhead), it's time to take a very close look at the NICs you are using = in the end hosts. A statistically significant difference would hint at = poor interrupt handling performance on the part of one or more of the = NICs and their associated device drivers. The intermediate switch overhead will be a constant (unless the switch = backplane becomes saturated from unrelated traffic). --lyndon --Apple-Mail=_DE3568EF-F524-45B3-92F1-C07102A1522F Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- iQIcBAEBCAAGBQJX4G3IAAoJEJCSmizucT9VZnQQALMucy5vTuLJZUitVi90UfdU OTQO/fFJmT7uuG7wK1nsrFf051bsHbCIEQ4rBP8kTa2PfnG0mpm2UYT6TV352x0Y R8yE3GJ19EFrc31t1NRqGdt2SNcndTAMGEJVOzXbPYNOrocB/adOVYxJ7HeVFIwK BDRezxdrBA40pqGD0cbE/d61A664C6CVQvJPYS9VgDKAeO3G6aScuidkI0sCdcFS qfJ3xji+4UftOfkIcmY6z2H+jhBckOu2kYeBMbN+S5eTjOc7xoWww5RmlIcVshPg 5e8kgm/M3X023p1gu2LRtQTok1JO3hEWb8mXbkj3zaP1UDDIhVe+MvvLjjnVFGks ZMCtDbFSt/fItkXKFxFTqc7HlPiv5Lkr7l+5lwkvZExtL3IYYXeviDuNV+VB45AR ln/whGc2b/CEgfon247LFpEEWS8a5uq8EW9GeWVcuIC07jloK/Bbn8J0xj72RUYP VpRuqUrtgx7BVAk+6H8sw3QavCYVvYg49nogS6gTP/bvstVzMF9C3E+om1R0/2Yq iH/QLUGj27m3uPaMptSvXoINt6rYFMBsBOZV8dtUymIg7vP/lCoBGy7f7VW/Uv11 4gebadhm2VnHEdq0qD73CZsI2KHBWmaHWEeVeJUIk+0QmX1F5P7HRw4pD1yd+bpa okAgmLRI4qGnoCZmnMoA =J1Ph -----END PGP SIGNATURE----- --Apple-Mail=_DE3568EF-F524-45B3-92F1-C07102A1522F--