Date: Mon, 19 Sep 2016 15:59:20 -0700 From: Lyndon Nerenberg <lyndon@orthanc.ca> To: Slawa Olhovchenkov <slw@zxy.spb.ru> Cc: FreeBSD Stable <freebsd-stable@freebsd.org> Subject: Re: LAGG and Jumbo Frames Message-ID: <42A03EA9-7F8E-446E-B430-7431AB9CE2E6@orthanc.ca> In-Reply-To: <20160919220812.GG2960@zxy.spb.ru> References: <48926c6013f938af832c17e4ad10b232@dweimer.net> <alpine.BSF.2.20.1609191326280.93154@orthanc.ca> <04c9065ee4a780c6f8986d1b204c4198@dweimer.net> <alpine.BSF.2.20.1609191419030.93154@orthanc.ca> <20160919220812.GG2960@zxy.spb.ru>
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--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 <slw@zxy.spb.ru> = 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--
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