From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga06.intel.com (mga06.intel.com [134.134.136.31]) by dpdk.org (Postfix) with ESMTP id 778143239 for ; Tue, 23 Aug 2016 14:23:36 +0200 (CEST) Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga104.jf.intel.com with ESMTP; 23 Aug 2016 05:23:35 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.28,565,1464678000"; d="scan'208";a="1040140060" Received: from yliu-dev.sh.intel.com (HELO yliu-dev) ([10.239.67.162]) by orsmga002.jf.intel.com with ESMTP; 23 Aug 2016 05:23:34 -0700 Date: Tue, 23 Aug 2016 20:33:21 +0800 From: Yuanhan Liu To: Thomas Monjalon Cc: dev@dpdk.org, Maxime Coquelin Message-ID: <20160823123321.GL30752@yliu-dev.sh.intel.com> References: <1471939839-29778-1-git-send-email-yuanhan.liu@linux.intel.com> <1471939839-29778-7-git-send-email-yuanhan.liu@linux.intel.com> <2052249.1FX31XPDFZ@xps13> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2052249.1FX31XPDFZ@xps13> User-Agent: Mutt/1.5.23 (2014-03-12) Subject: Re: [dpdk-dev] [PATCH 6/6] examples/vhost: add an option to enable Tx zero copy X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 23 Aug 2016 12:23:36 -0000 On Tue, Aug 23, 2016 at 11:31:08AM +0200, Thomas Monjalon wrote: > 2016-08-23 16:10, Yuanhan Liu: > > One thing worth noting while using Tx zero copy is the nb_tx_desc has > > to be small enough so that the eth driver will hit the mbuf free > > threshold easily and thus free mbuf more frequently. > > > > The reason behind that is, when Tx zero copy is enabled, guest Tx used > > vring will be updated only when corresponding mbuf is freed. If mbuf is > > not freed frequently, the guest Tx vring could be starved. > > I think you should explain this behaviour in the doc of the vhost flag. Agreed. Will do it in v2. --yliu