From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by inbox.dpdk.org (Postfix) with ESMTP id 6AE76A0613 for ; Fri, 30 Aug 2019 10:48:57 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id 178B61E8D1; Fri, 30 Aug 2019 10:48:56 +0200 (CEST) Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id E4E801E8CF for ; Fri, 30 Aug 2019 10:48:54 +0200 (CEST) Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 23EF2308A968; Fri, 30 Aug 2019 08:48:54 +0000 (UTC) Received: from [10.36.112.16] (ovpn-112-16.ams2.redhat.com [10.36.112.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EBBA25D772; Fri, 30 Aug 2019 08:48:52 +0000 (UTC) To: Matan Azrad , Noa Ezra Cc: "dev@dpdk.org" , Tiwei Bie 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> <59bce0c1-6f04-b743-c5fc-508b30e42075@redhat.com> <01a391c2-f68d-38fc-909b-3fc06100d1f7@redhat.com> <81735ee1-645d-286b-4516-64755fd07c94@redhat.com> <00a5fe75-4df7-5bf7-55f9-1b18aba4506c@redhat.com> From: Maxime Coquelin Openpgp: preference=signencrypt Autocrypt: addr=maxime.coquelin@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Fri, 30 Aug 2019 08:48:54 +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 6/27/19 7:04 AM, Matan Azrad wrote: > > > From: Maxime Coquelin >>>>>> For functional reasons, I agree. So I that's why I agree with your >>>>>> tso patch as the application has to support it, but that's not the >>>>>> case of the mergeable buffers features. >>>>> >>>>> Performance reasons are not good enough? >>>> >>>> No, that's not what I mean. >>>> I mean that the application should be able to disable a feature when >>>> it does not meet the functional requirement. >>>> >>>> For performance tuning, the qemu way is available, and enough. >>>> >>> >>> I think that this is the point we are not agree on. >>> >>> I think that application may want to disable the feature in some cases >>> because of performance reasons (maybe others too), And in some other >> cases to work with the feature. >>> >>> So, it makes sense IMO to let the application to decide what it wants >> without any concern about the QEMU configuration. >>> >>> Why to not allow to the PMD user to do it by the application (using prob >> parameters)? >> >> I think we should restrict the Virtio features from the Vhost PMD parameter >> at as min as possible, only to ensure compatibility with the application >> (iommu, postcopy, tso, ...). One problem I see with providing the possibility >> to change any Virtio feature at runtime is reconnection. >> >> For example, you start your application with enabling mergeable buffers, >> stop it and restart it without the feature enabled by the application. >> As the negotiation with the driver is not done again at reconnect time, Qemu >> will fail. > > Looks like you are describing a new issue in the vhost PMD, it must close the connection when the PMD is closed\removed. > So, every probe(hotplug add) it will start from scratch. > No, you can close the application and restart it for example without having to restart the guest. In this case, the feature negotiation is not done again. So I remain convinced we should not provide the possibility to disable any feature that is not dependent on the application. Megeable buffers is not dependent on the application, as it is only related to the ring implementation, and it is supported by the DPDK Vhost library. Regards, Maxime