From owner-freebsd-questions@FreeBSD.ORG Wed Aug 6 13:36:29 2008 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id B83CB1065670 for ; Wed, 6 Aug 2008 13:36:29 +0000 (UTC) (envelope-from yonyossef.lists@gmail.com) Received: from yw-out-2324.google.com (yw-out-2324.google.com [74.125.46.31]) by mx1.freebsd.org (Postfix) with ESMTP id 724CE8FC19 for ; Wed, 6 Aug 2008 13:36:29 +0000 (UTC) (envelope-from yonyossef.lists@gmail.com) Received: by yw-out-2324.google.com with SMTP id 9so1463691ywe.13 for ; Wed, 06 Aug 2008 06:36:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:to :subject:mime-version:content-type; bh=xAxV9cvNfsobteCFnNAbZKYlrkQaIN5sSdKGiDIPD2U=; b=i5wkIlOQ1ZPsUy2y7jZZFvmRih3TUvdWfckvjDeClZiSPZySM1phrXs4ZcU1lEV5X5 Wpj1s9kyCi3ve6iERvp0PzB1WoKGBGiRBAa6FbJeYjTR/i9/o0RAzzwKcm4s5wYB7r/o 61HrJdgtsIm6j3/WHzlFp42vVLSujCkyj8I24= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:mime-version:content-type; b=TyDczeg6p969sELHCLEFQ7Z+IjTLFlUhknFYmwKT8ftrMTZhCfjWvHJG1NZ2peJxqQ xjDR66udXK1jdAfIWVZ41ni1nzKYt4f+7DN4414gCd6r/cvQ5/ILVvYk561IMbreVCyp 7ytysgJqSOZwOPTDx/dfewurhVHOBhCP2kNLk= Received: by 10.151.109.11 with SMTP id l11mr3436769ybm.13.1218029788856; Wed, 06 Aug 2008 06:36:28 -0700 (PDT) Received: by 10.151.84.2 with HTTP; Wed, 6 Aug 2008 06:36:28 -0700 (PDT) Message-ID: <20def4870808060636h2d8e9082td1e486a41f9506aa@mail.gmail.com> Date: Wed, 6 Aug 2008 16:36:28 +0300 From: "Yony Yossef" To: freebsd-questions@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Subject: Long mbuf chains X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 06 Aug 2008 13:36:29 -0000 Hi All I'm working on an Ethernet driver for FreeBSD 7.0. Taking network performance numbers I encountered very long mbuf chains on the sender side. The symptom is constant, always during iperf/netperf TCP stream tests with message sizes of 128 bytes (>200 mbufs per chain), 1024 bytes (30-60 mbufs per chain) and 2048 bytes. My problem is that long chains require some kind of defragmentation/cutting before it can be properly DMAd. This is pretty a expansive operation. 1. Is there a way of tuning the OS for sending limited length mbuf chains? I thought setting "net.inet.ip.maxfragsperpacket" would do it but it doesn't. 2. Is there a better way of handling this issue? Thanks, Yony