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From: Morten Brørup <mb@smartsharesystems.com>
To: "Jeff Guo" <jia.guo@intel.com>,
	"Thomas Monjalon" <thomas@monjalon.net>,
	"Ferruh Yigit" <ferruh.yigit@intel.com>,
	"Andrew Rybchenko" <arybchenko@solarflare.com>
Cc: <qiming.yang@intel.com>, <beilei.xing@intel.com>,
	<wei.zhao1@intel.com>, <qi.z.zhang@intel.com>,
	<jingjing.wu@intel.com>, <bruce.richardson@intel.com>,
	<dev@dpdk.org>, <helin.zhang@intel.com>, <ferruh.yigit@intel.com>,
	<barbette@kth.se>
Subject: [dpdk-dev] [RFC] ethdev: rte_eth_rx_burst() requirements for nb_pkts
Date: Thu, 27 Aug 2020 10:40:11 +0200
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35C61257@smartserver.smartshare.dk> (raw)
In-Reply-To: <20200827075452.1751-1-jia.guo@intel.com>

Jeff and Ethernet API maintainers Thomas, Ferruh and Andrew,

I'm hijacking this patch thread to propose a small API modification that prevents unnecessarily performance degradations.

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Jeff Guo
> Sent: Thursday, August 27, 2020 9:55 AM
> 
> The limitation of burst size in vector rx was removed, since it should
> retrieve as much received packets as possible. And also the scattered
> receive path should use a wrapper function to achieve the goal of
> burst maximizing.
> 
> This patch set aims to maximize vector rx burst for for
> ixgbe/i40e/ice/iavf PMDs.
> 

Now I'm going to be pedantic and say that it still doesn't conform to the rte_eth_rx_burst() API, because the API does not specify any minimum requirement for nb_pkts.

In theory, that could also be fixed in the driver by calling the non-vector function from the vector functions if nb_pkts is too small for the vector implementation.

However, I think that calling rte_eth_rx_burst() with a small nb_pkts is silly and not in the spirit of DPDK, and introducing an additional comparison for a small nb_pkts in the driver vector functions would degrade their performance (only slightly, but anyway).

Instead, I propose that the rte_eth_rx_burst() API is updated with a minimum requirement for nb_pkts. This minimum requirement should be supported by all Ethernet drivers, instead of having minimum requirements for nb_pkts depending on driver and vector function.


I also have a small comment about the description for all the main rx functions:

+/**
+ * vPMD receive routine that reassembles scattered packets.
+ * Main receive routine that can handle arbitrary burst sizes
+ * Notice:
+ * - nb_pkts < RTE_I40E_DESCS_PER_LOOP, just return no packet
+ */

It says "can handle arbitrary burst sizes", but bears a notice that it really cannot. So please remove that line from all these functions.


Med venlig hilsen / kind regards
- Morten Brørup

  parent reply	other threads:[~2020-08-27  8:40 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-27  7:54 [dpdk-dev] [PATCH v1 0/4] maximize vector rx burst for PMDs Jeff Guo
2020-08-27  7:54 ` [dpdk-dev] [PATCH v1 1/4] net/ixgbe: maximize vector rx burst for ixgbe Jeff Guo
2020-08-27  7:54 ` [dpdk-dev] [PATCH v1 2/4] net/i40e: maximize vector rx burst for i40e Jeff Guo
2020-08-27  7:54 ` [dpdk-dev] [PATCH v1 3/4] net/ice: maximize vector rx burst for ice Jeff Guo
2020-08-27  7:54 ` [dpdk-dev] [PATCH v1 4/4] net/iavf: maximize vector rx burst for iavf Jeff Guo
2020-08-27  8:40 ` Morten Brørup [this message]
2020-08-27  9:09   ` [dpdk-dev] [RFC] ethdev: rte_eth_rx_burst() requirements for nb_pkts Bruce Richardson
2020-08-27  9:31     ` Morten Brørup
2020-08-27  9:43       ` Bruce Richardson
2020-08-27 10:13         ` [dpdk-dev] [RFC] ethdev: rte_eth_rx_burst() requirements fornb_pkts Morten Brørup
2020-08-27 11:41           ` Bruce Richardson
2020-08-28  9:03             ` Morten Brørup
2020-08-28 10:07               ` Bruce Richardson
2020-08-28 10:50                 ` Morten Brørup
2020-08-29 10:15                 ` Morten Brørup
2020-09-09  6:36 ` [dpdk-dev] [PATCH v3 0/5] fix vector rx burst for PMDs Jeff Guo
2020-09-09  6:36   ` [dpdk-dev] [PATCH v3 1/5] net/iavf: fix vector rx burst for iavf Jeff Guo
2020-09-09  6:36   ` [dpdk-dev] [PATCH v3 2/5] net/ixgbe: fix vector rx burst for ixgbe Jeff Guo
     [not found]     ` <VI1PR0802MB23518C6B517B6EAD8E018CD49E260@VI1PR0802MB2351.eurprd08.prod.outlook.com>
2020-09-09  9:54       ` [dpdk-dev] 回复: " Feifei Wang
2020-09-09  6:36   ` [dpdk-dev] [PATCH v3 3/5] net/i40e: fix vector rx burst for i40e Jeff Guo
2020-09-09  6:36   ` [dpdk-dev] [PATCH v3 4/5] net/ice: fix vector rx burst for ice Jeff Guo
2020-09-15  7:10     ` Han, YingyaX
2020-09-09  6:36   ` [dpdk-dev] [PATCH v3 5/5] net/fm10k: fix vector rx burst for fm10k Jeff Guo
2020-09-09  6:45   ` [dpdk-dev] [PATCH v3 0/5] fix vector rx burst for PMDs Wang, Haiyue
2020-09-09  7:03     ` Guo, Jia
2020-09-09  7:05       ` Wang, Haiyue
2020-09-09  7:43         ` Morten Brørup
2020-09-09  7:55           ` Wang, Haiyue
2020-09-09  8:01             ` Guo, Jia
2020-09-17  7:58 ` [dpdk-dev] [PATCH v4 " Jeff Guo
2020-09-17  7:58   ` [dpdk-dev] [PATCH v4 1/5] net/iavf: fix vector rx burst for iavf Jeff Guo
2020-09-17  7:58   ` [dpdk-dev] [PATCH v4 2/5] net/ixgbe: fix vector rx burst for ixgbe Jeff Guo
2020-09-17  7:58   ` [dpdk-dev] [PATCH v4 3/5] net/i40e: fix vector rx burst for i40e Jeff Guo
2020-09-17  7:58   ` [dpdk-dev] [PATCH v4 4/5] net/ice: fix vector rx burst for ice Jeff Guo
2020-09-17 11:03     ` Zhang, Qi Z
2020-09-18  3:20       ` Guo, Jia
2020-09-18  3:41         ` Zhang, Qi Z
2020-09-18  4:41           ` Guo, Jia
2020-09-18  5:39             ` Zhang, Qi Z
2020-09-17  7:58   ` [dpdk-dev] [PATCH v4 5/5] net/fm10k: fix vector rx burst for fm10k Jeff Guo
2020-10-16  9:44 ` [dpdk-dev] [PATCH v5 0/5] fix vector rx burst for PMDs Jeff Guo
2020-10-16  9:44   ` [dpdk-dev] [PATCH v5 1/5] net/ixgbe: fix vector rx burst for ixgbe Jeff Guo
2020-10-16  9:44   ` [dpdk-dev] [PATCH v5 2/5] net/i40e: fix vector rx burst for i40e Jeff Guo
2020-10-16  9:44   ` [dpdk-dev] [PATCH v5 3/5] net/ice: fix vector rx burst for ice Jeff Guo
2020-10-16  9:44   ` [dpdk-dev] [PATCH v5 4/5] net/fm10k: fix vector rx burst for fm10k Jeff Guo
2020-10-16  9:44   ` [dpdk-dev] [PATCH v5 5/5] net/iavf: fix vector rx burst for iavf Jeff Guo
2020-10-23  5:09     ` Ling, WeiX
2020-10-23 10:11   ` [dpdk-dev] [PATCH v5 0/5] fix vector rx burst for PMDs Zhang, Qi Z

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