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Thu, 26 Mar 2020 04:47:58 -0400 X-MC-Unique: CFvapnb3MgKeM4vDzqtfZw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 82982801E70; Thu, 26 Mar 2020 08:47:57 +0000 (UTC) Received: from [10.36.110.23] (unknown [10.36.110.23]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2107B19C70; Thu, 26 Mar 2020 08:47:55 +0000 (UTC) To: "Hu, Jiayu" , "dev@dpdk.org" Cc: "Ye, Xiaolong" , "Wang, Zhihong" References: <1584436885-18651-1-git-send-email-jiayu.hu@intel.com> <370798e0-b006-4a33-d8d9-1aea7bf4af49@redhat.com> <33221483053a41e8bd8d4bd0cb582634@intel.com> <63c79431-96bf-79e9-fb75-1714e194257f@redhat.com> <39c02e0f982a4ce88ae421e6a9c7d26e@intel.com> <2f98b893-c486-6b0d-d824-61a5fef994cf@redhat.com> <1007246585054daca2afce895ac9f875@intel.com> From: Maxime Coquelin Autocrypt: addr=maxime.coquelin@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <1007246585054daca2afce895ac9f875@intel.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Subject: Re: [dpdk-dev] [PATCH 0/4] Support DMA-accelerated Tx operations for vhost-user PMD 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 3/26/20 9:25 AM, Hu, Jiayu wrote: > Hi Maxime, >=20 >> -----Original Message----- >> From: Maxime Coquelin >> Sent: Thursday, March 26, 2020 3:53 PM >> To: Hu, Jiayu ; dev@dpdk.org >> Cc: Ye, Xiaolong ; Wang, Zhihong >> >> Subject: Re: [PATCH 0/4] Support DMA-accelerated Tx operations for vhost= - >> user PMD >> >> Hi Jiayu, >> >> On 3/19/20 12:47 PM, Hu, Jiayu wrote: >> >>>> >>>> Ok, so what about: >>>> >>>> Introducing a pair of callbacks in struct virtio_net for DMA enqueue a= nd >>>> dequeue. >>>> >>>> lib/librte_vhost/ioat.c which would implement dma_enqueue and >>>> dma_dequeue callback for IOAT. As it will live in the vhost lib >>>> directory, it will be easy to refactor the code to share as much as >>>> possible and so avoid code duplication. >>>> >>>> In rte_vhost_enqueue/dequeue_burst, if the dma callback is set, then >>>> call it instead of the SW datapath. It adds a few cycle, but this is >>>> much more sane IMHO. >>> >>> The problem is that current semantics of rte_vhost_enqueue/dequeue API >>> are conflict with I/OAT accelerated data path. To improve the performan= ce, >>> the I/OAT works in an asynchronous manner, where the CPU just submits >>> copy jobs to the I/OAT without waiting for its copy completion. For >>> rte_vhost_enqueue_burst, users cannot reuse enqueued pktmbufs when >> it >>> returns, as the I/OAT may still use them. For rte_vhost_dequeue_burst, >>> users will not get incoming packets as the I/OAT is still performing pa= cket >>> copies. As you can see, when enabling I/OAT acceleration, the semantics= of >>> the two API are changed. If we keep the same API name but changing thei= r >>> semantic, this may confuse users, IMHO. >> >> Ok, so it is basically the same as zero-copy for dequeue path, right? >> If a new API is necessary, then it would be better to add it in Vhost >> library for async enqueue/dequeue. >> It could be used also for Tx zero-copy, and so the sync version would >> save some cycles as we could remove the zero-copy support there. >> >> What do you think? >=20 > Yes, you are right. The better way is to provide new API with asynchronou= s > semantics in vhost library. In addition, the vhost library better provide= s DMA > operation callbacks to avoid using vender specific API. The asynchronous = API may > look like rte_vhost_try_enqueue_burst() and rte_vhost_get_completed_packe= ts(). > The first one is to perform enqueue logic, and the second one is to retur= n > pktmbufs whose all copies are completed to users. How do you think? That looks good to me, great! The only think is the naming of the API. I need t think more about it, but it does not prevent to start working on the implementation. Regarding the initialization, I was thinking we could introduce new flags to rte_vhost_driver_register: - RTE_VHOST_USER_TX_DMA - RTE_VHOST_USER_RX_DMA Well, only Tx can be implemented for now, but the Rx flag can be reserved. The thing I'm not clear is when no DMA is available, how do we fallback to the sync API. Should the user still call rte_vhost_try_enqueue_burst(), but if no DMA, it will call the rte_vhost_enqueue_burst() directly and then rte_vhost_get_completed_packets() will return all the mbufs? Thanks, Maxime > Thanks, > Jiayu >=20 >> >> I really object to implement vring handling into the Vhost PMD, this is >> the role of the Vhost library. >> >> Thanks, >> Maxime >=20