From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by dpdk.space (Postfix) with ESMTP id E54D1A0471 for ; Thu, 20 Jun 2019 09:19:29 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id D50201D013; Thu, 20 Jun 2019 09:19:28 +0200 (CEST) Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id 2FB0C1D011 for ; Thu, 20 Jun 2019 09:19:27 +0200 (CEST) Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 7ED76C18B2D2; Thu, 20 Jun 2019 07:19:26 +0000 (UTC) Received: from [10.36.112.46] (ovpn-112-46.ams2.redhat.com [10.36.112.46]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9615B1001DCB; Thu, 20 Jun 2019 07:19:25 +0000 (UTC) To: Matan Azrad , Noa Ezra Cc: "dev@dpdk.org" References: <1560924825-220648-1-git-send-email-noae@mellanox.com> <1560924825-220648-3-git-send-email-noae@mellanox.com> <29a8bedb-2363-d595-001b-577fdfc7318c@redhat.com> From: Maxime Coquelin Message-ID: <59bce0c1-6f04-b743-c5fc-508b30e42075@redhat.com> Date: Thu, 20 Jun 2019 09:19:23 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Thu, 20 Jun 2019 07:19:26 +0000 (UTC) Subject: Re: [dpdk-dev] [PATCH 2/2] net/vhost: support mrg-rxbuf disabling X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On 6/20/19 8:52 AM, Matan Azrad wrote: > Hi all > >> -----Original Message----- >> From: Noa Ezra >> Sent: Thursday, June 20, 2019 8:58 AM >> To: Maxime Coquelin >> Cc: Matan Azrad ; dev@dpdk.org >> Subject: RE: [PATCH 2/2] net/vhost: support mrg-rxbuf disabling >> >> Hi Maxime, >> Thanks for your comment, please see below. >> >>> -----Original Message----- >>> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com] >>> Sent: Wednesday, June 19, 2019 12:10 PM >>> To: Noa Ezra >>> Cc: Matan Azrad ; dev@dpdk.org >>> Subject: Re: [PATCH 2/2] net/vhost: support mrg-rxbuf disabling >>> >>> Hi Noa, >>> >>> On 6/19/19 8:13 AM, Noa Ezra wrote: >>>> Rx mergeable buffers is a virtio feature that allows chaining of >>>> multiple virtio descriptors to handle large packet size. >>>> This behavior is supported and enabled by default, however in case >>>> the user knows that rx mergeable buffers are not needed, he can >>>> disable the feature. >>>> The user should also set mrg_rxbuf=off in virtual machine's xml. >>> >>> I'm not sure to understand why it is needed, as the vhost-user library >>> supports the feature, it's better to let it being advertised. >>> >>> As you say, it is up to the user to disable it in the VM's XML. >>> Done this way, the feature won't be negotiated. >>> >> I agree with you, I'll remove this patch from the series. > > Are you sure that no performance impact exists for redundant merg-rx-buf configuration here? I'm not sure to understand what you mean, could you please elaborate? > What if the second side want it and the current side no? The feature won't be negotiated, assuming it has been disabled in QEMU cmdline (or via libvirt). > It may be that the vhost PMD user may want to disable it to save performance from some reasons, no? > Then this user should disable it at QEMU level. Regards, Maxime