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b=jVj/X//WB/1PRug5QlE6krm4VZZpMLDmsN/7H8mHd1CPju6dl0TsL6yWm5A8PAFsCDKjas7eo/iU/AorwnmgrIUSidwI4ljIOoURzCUvT1/ZXO3+TV7SI1zN64JZjJzb7qWFRKY9ajCgD+MlpJpNARuP//fZaqdSykV4sFcXfU0= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from CH2PR12MB4294.namprd12.prod.outlook.com (2603:10b6:610:a9::11) by IA0PR12MB8646.namprd12.prod.outlook.com (2603:10b6:208:489::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6954.21; Thu, 2 Nov 2023 17:05:48 +0000 Received: from CH2PR12MB4294.namprd12.prod.outlook.com ([fe80::2569:edb2:670f:816f]) by CH2PR12MB4294.namprd12.prod.outlook.com ([fe80::2569:edb2:670f:816f%6]) with mapi id 15.20.6954.019; Thu, 2 Nov 2023 17:05:48 +0000 Message-ID: <37297af0-8b18-43e1-b7ad-9ed81e733599@amd.com> Date: Thu, 2 Nov 2023 17:05:38 +0000 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 0/3] introduce maximum Rx buffer size Content-Language: en-US To: =?UTF-8?Q?Morten_Br=C3=B8rup?= , "lihuisong (C)" , Stephen Hemminger Cc: dev@dpdk.org, thomas@monjalon.net, andrew.rybchenko@oktetlabs.ru, liuyonglong@huawei.com References: <20230808040234.12947-1-lihuisong@huawei.com> <20231028014847.27149-1-lihuisong@huawei.com> <20231029084838.122acb9e@hermes.local> <20231030114850.799f2bce@fedora> <20231031084017.64b9f342@fedora> <20231101090847.105f0fa1@fedora> <177b8c04-a8f5-3889-dd26-474122b0be50@huawei.com> <2e2a17cc-6dc2-4ce2-bed8-d3e7239b83ff@amd.com> <98CBD80474FA8B44BF855DF32C47DC35E9EFCB@smartserver.smartshare.dk> From: Ferruh Yigit Autocrypt: addr=ferruh.yigit@amd.com; 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It's a common feature for all >> PMDs. >>>>>> It would make sense then to have max_rx_bufsize set to 16K by >> default >>>>>> in ethdev, and PMD could then raise/lower based on hardware. >>>>> It is not appropriate to set to 16K by default in ethdev layer. >>>>> Because I don't see any check for the upper bound in some driver, >> like >>>>> axgbe, enetc and so on. >>>>> I'm not sure if they have no upper bound. >>>>> And some driver's maximum buffer size is "16384(16K) - 128" >>>>> So it's better to set to UINT32_MAX by default. >>>>> what do you think? >>>> The goal is always giving application a working upper bound, and >>>> enforcing >>>> that as much as possible in ethdev layer. It doesnt matter which >> pattern >>>> does that.  Fortunately, telling application an incorrect answer is >>>> not fatal. >>>> If over estimated, application pool would be wasting space. >>>> If under estimated, application will get more fragmented packets. >>> I know what you mean. >>> If we set UINT32_MAX, it just means that driver don't report this >> upper >>> bound. >>> This is also a very common way of handling. And it has no effect on >> the >>> drivers that doesn't report this value. >>> On the contrary, if we set a default value (like 16K) in ethdev, user >>> may be misunderstood and confused by that, right? >>> After all, this isn't the real upper bound of all drivers. And this >>> fixed default value may affect the behavior of some driver that I >> didn't >>> find their upper bound. >>> So I'd like to keep it as UINT32_MAX. >>> >> >> >> Hi Stephen, Morten, >> >> I saw scattered Rx mentioned, there may be some misalignment, >> the purpose of the patch is not to enable application to set as big as >> possible mbuf size, so that application can escape from parsing >> multi-segment mbufs. >> Indeed application can provide a large mbuf anyway, to have same >> result, >> without knowing this information. >> >> Main motivation is other way around, device may have restriction on >> buffer size that a single descriptor can address, independent from >> scattered Rx used, if mbuf size is bigger than this device limit, each >> mbuf will have some unused space. >> Patch has intention to inform this max per mbuf/descriptor buffer size, >> so that application doesn't allocate bigger mbuf and waste memory. > > Good point! > > Let's categorize this patch series as a memory optimization for applications that support jumbo frames, but are trying to avoid (or reduce) scattered RX. :-) > It is a memory optimization patch, but again nothing to do with jumbo frames or scattered Rx.