From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Sidorenko Subject: Re: Receive offloads, small RCVBUF and zero TCP window Date: Mon, 28 Nov 2016 16:14:04 -0500 Message-ID: <15427752.RvQkb5CQdb@zbook> References: <2080597.A38JFJZ1AD@zbook> <20161128.155459.1527519991492144879.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: netdev@vger.kernel.org To: David Miller Return-path: Received: from g9t1613g.houston.hpe.com ([15.241.32.99]:31431 "EHLO g9t1613g.houston.hpe.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932675AbcK1VOJ (ORCPT ); Mon, 28 Nov 2016 16:14:09 -0500 Received: from g2t2354.austin.hpe.com (g2t2354.austin.hpe.com [15.233.44.27]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by g9t1613g.houston.hpe.com (Postfix) with ESMTPS id 0899F6125D for ; Mon, 28 Nov 2016 21:14:08 +0000 (UTC) In-Reply-To: <20161128.155459.1527519991492144879.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On Monday, November 28, 2016 3:54:59 PM EST David Miller wrote: > From: Alex Sidorenko > Date: Mon, 28 Nov 2016 15:49:26 -0500 > > > Now the question is whether is is OK to have icsk->icsk_ack.rcv_mss > > larger than MTU. > > It absolutely is not OK. > > If VMWare wants to receive large frames for batching purposes it must > use GRO or similar to achieve that, not just send vanilla frames into > the stack which are larger than the device MTU. > As VMWare's vmxnet3 driver is open-sourced and part of generic kernel, do you think the problem is in that driver or elsewhere? I looked at vmxnet3 sources and see that it uses LRO/GRO subroutines. Unfortunately, I don't understand its logic enough to see whether they are doing anything incorrectly. Alex -- ------------------------------------------------------------------ Alex Sidorenko email: asid@hpe.com ERT Linux Hewlett-Packard Enterprise (Canada) ------------------------------------------------------------------