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Tue, 28 Apr 2020 11:40:12 -0400 X-MC-Unique: HLvUk7-6NZin2sIx1RRStw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9D860EC1A1; Tue, 28 Apr 2020 15:40:10 +0000 (UTC) Received: from [10.36.110.26] (unknown [10.36.110.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ECEB15D9E5; Tue, 28 Apr 2020 15:40:08 +0000 (UTC) To: "Liu, Yong" , "Ye, Xiaolong" , "Wang, Zhihong" Cc: "dev@dpdk.org" , Honnappa Nagarahalli , "jerinj@marvell.com" References: <20200313174230.74661-1-yong.liu@intel.com> <20200426021943.43158-1-yong.liu@intel.com> <20200426021943.43158-7-yong.liu@intel.com> <672a584a-46d1-c78b-7b21-9ed7bc060814@redhat.com> <86228AFD5BCD8E4EBFD2B90117B5E81E63546D0C@SHSMSX103.ccr.corp.intel.com> <86228AFD5BCD8E4EBFD2B90117B5E81E6354755C@SHSMSX103.ccr.corp.intel.com> <679f4dc1-a4ac-ab1b-a7b1-297d66158820@redhat.com> <86228AFD5BCD8E4EBFD2B90117B5E81E635476DC@SHSMSX103.ccr.corp.intel.com> <2c383833-c67f-c1fb-ea3f-c3802b24de79@redhat.com> <86228AFD5BCD8E4EBFD2B90117B5E81E63547785@SHSMSX103.ccr.corp.intel.com> From: Maxime Coquelin Autocrypt: addr=maxime.coquelin@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <86228AFD5BCD8E4EBFD2B90117B5E81E63547785@SHSMSX103.ccr.corp.intel.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [dpdk-dev] [PATCH v10 6/9] net/virtio: add vectorized packed ring Rx path 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 4/28/20 5:35 PM, Liu, Yong wrote: > > >> -----Original Message----- >> From: Maxime Coquelin >> Sent: Tuesday, April 28, 2020 10:50 PM >> To: Liu, Yong ; Ye, Xiaolong ; >> Wang, Zhihong >> Cc: dev@dpdk.org; Honnappa Nagarahalli >> ; jerinj@marvell.com >> Subject: Re: [PATCH v10 6/9] net/virtio: add vectorized packed ring Rx path >> >> >> >> On 4/28/20 4:43 PM, Liu, Yong wrote: >>> >>> >>>> -----Original Message----- >>>> From: Maxime Coquelin >>>> Sent: Tuesday, April 28, 2020 9:46 PM >>>> To: Liu, Yong ; Ye, Xiaolong >> ; >>>> Wang, Zhihong >>>> Cc: dev@dpdk.org; Honnappa Nagarahalli >>>> ; jerinj@marvell.com >>>> Subject: Re: [PATCH v10 6/9] net/virtio: add vectorized packed ring Rx >> path >>>> >>>> >>>> >>>> On 4/28/20 3:01 PM, Liu, Yong wrote: >>>>>>> Maxime, >>>>>>> Thanks for point it out, it will add extra cache miss in datapath. >>>>>>> And its impact on performance is around 1% in loopback case. >>>>>> Ok, thanks for doing the test. I'll try to run some PVP benchmarks >>>>>> on my side because when doing IO loopback, the cache pressure is >>>>>> much less important. >>>>>> >>>>>>> While benefit of vectorized path will be more than that number. >>>>>> Ok, but I disagree for two reasons: >>>>>> 1. You have to keep in mind than non-vectorized is the default and >>>>>> encouraged mode to use. Indeed, it takes a lot of shortcuts like not >>>>>> checking header length (so no error stats), etc... >>>>>> >>>>> Ok, I will keep non-vectorized same as before. >>>>> >>>>>> 2. It's like saying it's OK it degrades by 5% on $CPU_VENDOR_A >> because >>>>>> the gain is 20% on $CPU_VENDOR_B. >>>>>> >>>>>> In the case we see more degradation in real-world scenario, you might >>>>>> want to consider using ifdefs to avoid adding padding in the non- >>>>>> vectorized case, like you did to differentiate Virtio PMD to Virtio-user >>>>>> PMD in patch 7. >>>>>> >>>>> Maxime, >>>>> The performance difference is so slight, so I ignored for it look like a >>>> sampling error. >>>> >>>> Agree for IO loopback, but it adds one more cache line access per burst, >>>> which might be see in some real-life use cases. >>>> >>>>> It maybe not suitable to add new configuration for such setting which >>>> only used inside driver. >>>> >>>> Wait, the Virtio-user #ifdef is based on the defconfig options? How can >>>> it work since both Virtio PMD and Virtio-user PMD can be selected at the >>>> same time? >>>> >>>> I thought it was a define set before the headers inclusion and unset >>>> afterwards, but I didn't checked carefully. >>>> >>> >>> Maxime, >>> The difference between virtio PMD and Virtio-user PMD addresses is >> handled by vq->offset. >>> >>> When virtio PMD is running, offset will be set to buf_iova. >>> vq->offset = offsetof(struct rte_mbuf, buf_iova); >>> >>> When virtio_user PMD is running, offset will be set to buf_addr. >>> vq->offset = offsetof(struct rte_mbuf, buf_addr); >> >> Ok, but below is a build time check: >> >> +#ifdef RTE_VIRTIO_USER >> + __m128i flag_offset = _mm_set_epi64x(flags_temp, (uint64_t)vq- >>> offset); >> +#else >> + __m128i flag_offset = _mm_set_epi64x(flags_temp, 0); >> +#endif >> >> So how can it work for a single build for both Virtio and Virtio-user? >> > > Sorry, here is an implementation error. vq->offset should be used in descs_base for getting the iova address. > It will work the same as VIRTIO_MBUF_ADDR macro. > >>>>> Virtio driver can check whether virtqueue is using vectorized path when >>>> initialization, will use padded structure if it is. >>>>> I have added some tested code and now performance came back. Since >>>> code has changed in initialization process, it need some time for >> regression >>>> check. >>>> >>>> Ok, works for me. >>>> >>>> I am investigating a linkage issue with your series, which does not >>>> happen systematically (see below, it happens also with clang). David >>>> pointed me to some Intel patches removing the usage if __rte_weak, >>>> could it be related? >>>> >>> >>> I checked David's patch, it only changed i40e driver. Meanwhile attribute >> __rte_weak should still be in virtio_rxtx.c. >>> I will follow David's patch, eliminate the usage of weak attribute. >> >> Yeah, I meant below issue could be linked to __rte_weak, not that i40e >> patch was the cause of this problem. >> > > Maxime, > I haven't seen any build issue related to __rte_weak both with gcc and clang. Note that this build (which does not fail systematically) is when using binutils 2.30, which cause AVX512 support to be disabled. > Thanks, > Marvin >