From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ferruh Yigit Subject: Re: [PATCH v3 03/10] net/enic: heed the requested max Rx packet size Date: Fri, 9 Mar 2018 15:57:46 +0000 Message-ID: References: <20180306014634.28398-2-johndale@cisco.com> <20180308024702.25974-1-johndale@cisco.com> <20180308024702.25974-4-johndale@cisco.com> <2601191342CEEE43887BDE71AB97725890F22461@irsmsx105.ger.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: "dev@dpdk.org" , Hyong Youb Kim To: "Ananyev, Konstantin" , John Daley Return-path: Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by dpdk.org (Postfix) with ESMTP id 8129A4CBD for ; Fri, 9 Mar 2018 16:57:49 +0100 (CET) In-Reply-To: <2601191342CEEE43887BDE71AB97725890F22461@irsmsx105.ger.corp.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 3/9/2018 3:51 PM, Ananyev, Konstantin wrote: > > Hi everyone, > >> -----Original Message----- >> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Ferruh Yigit >> Sent: Friday, March 9, 2018 3:04 PM >> To: John Daley >> Cc: dev@dpdk.org; Hyong Youb Kim >> Subject: Re: [dpdk-dev] [PATCH v3 03/10] net/enic: heed the requested max Rx packet size >> >> On 3/8/2018 2:46 AM, John Daley wrote: >>> From: Hyong Youb Kim >>> >>> Currently, enic completely ignores the requested max Rx packet size >>> (rxmode.max_rx_pkt_len). The desired behavior is that the NIC hardware >>> drops packets larger than the requested size, even though they are >>> still smaller than MTU. >> >> Your description looks reasonable but is there reason of two levels of limits, >> max_rx_pkt_len and MTU, why not just use MTU. There is already a mail thread to >> clarify max_rx_pkt_len [1]. >> >> Is this work based on an application that uses max_rx_pkt_len and to make PMD >> compatible with that application? If so we can continue with patch, but if the >> patch is to implement DPDK properly I suggest postponing this until >> max_rx_pkt_len clarified. >> >> [1] >> https://dpdk.org/ml/archives/dev/2018-March/092178.html > > I think there are quite a lot apps these days that might rely on setting MTU via > rxmode.max_rx_pkt_len. > I think we need to support them till we (ever) deprecate rxmode.max_rx_pkt_len. Right. I was trying to save effort in case something changes related max_rx_pkt_len, but since it is not clear yet, will continue with this patch. > Konstantin > >> >>> >>> Cisco VIC does not have such a feature. But, we can accomplish a >>> similar (not same) effect by reducing the size of posted receive >>> buffers. Packets larger than the posted size get truncated, and the >>> receive handler drops them. This is also how the kernel enic driver >>> enforces the Rx side MTU. >>> >>> This workaround works only when scatter mode is *not* used. When >>> scatter is used, there is currently no way to support >>> rxmode.max_rx_pkt_len, as the NIC always receives packets up to MTU. >>> >>> For posterity, add a copious amount of comments regarding the >>> hardware's drop/receive behavior with respect to max/current MTU. >>> >>> Signed-off-by: Hyong Youb Kim >>> Reviewed-by: John Daley >> >> <...> >