From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxime Coquelin Subject: Re: [PATCH v2] doc: add driver limitation for vhost dequeue zero copy Date: Tue, 6 Mar 2018 09:57:07 +0100 Message-ID: <156edfa4-da00-70c8-f3e8-a034f1db5ae2@redhat.com> References: <1519483453-12613-1-git-send-email-junjie.j.chen@intel.com> <1519723268-28723-1-git-send-email-junjie.j.chen@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: dev@dpdk.org To: Junjie Chen , yliu@fridaylinux.org, jianfeng.tan@intel.com Return-path: Received: from mx1.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by dpdk.org (Postfix) with ESMTP id 2EE1923D for ; Tue, 6 Mar 2018 09:57:12 +0100 (CET) In-Reply-To: <1519723268-28723-1-git-send-email-junjie.j.chen@intel.com> Content-Language: en-US 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 02/27/2018 10:21 AM, Junjie Chen wrote: > In vhost-switch example, when binding nic to vfio-pci, dequeue zero > copy cannot work in VM2NIC mode due to no iommu dma mapping is setup > for guest memory currently. > > Signed-off-by: Junjie Chen > --- > Changes in V2: > - add doc in vhost lib > > doc/guides/prog_guide/vhost_lib.rst | 3 +++ > doc/guides/sample_app_ug/vhost.rst | 5 ++++- > 2 files changed, 7 insertions(+), 1 deletion(-) > > diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst > index 18227b6..bdf77d6 100644 > --- a/doc/guides/prog_guide/vhost_lib.rst > +++ b/doc/guides/prog_guide/vhost_lib.rst > @@ -83,6 +83,9 @@ The following is an overview of some key Vhost API functions: > of those segments, thus the fewer the segments, the quicker we will get > the mapping. NOTE: we may speed it by using tree searching in future. > > + * zero copy does not work when using vfio-pci driver currently, this is > + because we don't setup iommu dma mapping for guest memory. > + I guess that it should work with vfio-pci in noiommu mode? Maybe worth to clarify. > - ``RTE_VHOST_USER_IOMMU_SUPPORT`` > > IOMMU support will be enabled when this flag is set. It is disabled by > diff --git a/doc/guides/sample_app_ug/vhost.rst b/doc/guides/sample_app_ug/vhost.rst > index a4bdc6a..840c1fd 100644 > --- a/doc/guides/sample_app_ug/vhost.rst > +++ b/doc/guides/sample_app_ug/vhost.rst > @@ -147,7 +147,10 @@ retries on an RX burst, it takes effect only when rx retry is enabled. The > default value is 15. > > **--dequeue-zero-copy** > -Dequeue zero copy will be enabled when this option is given. > +Dequeue zero copy will be enabled when this option is given, it is worth to > +note that if NIC is binded to vfio-pci driver, dequeue zero copy cannot work > +at VM2NIC mode (vm2vm=0) due to currently we don't setup iommu dma mapping for > +guest memory. > > **--vlan-strip 0|1** > VLAN strip option is removed, because different NICs have different behaviors >