From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: rte_eth_rx_queue_count accuracy Date: Mon, 21 Sep 2015 15:41:30 -0700 Message-ID: <20150921154130.5b5dd845@urahara> References: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: dev To: Alejandro Lucero Return-path: Received: from mail-pa0-f49.google.com (mail-pa0-f49.google.com [209.85.220.49]) by dpdk.org (Postfix) with ESMTP id C93B48D89 for ; Tue, 22 Sep 2015 00:41:17 +0200 (CEST) Received: by padhy16 with SMTP id hy16so128524172pad.1 for ; Mon, 21 Sep 2015 15:41:17 -0700 (PDT) In-Reply-To: List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Fri, 18 Sep 2015 11:33:36 +0100 Alejandro Lucero wrote: > I have seen the API definition says nothing about accuracy but some PMD > implementations sacrifice accuracy for the sake of performance. If I'm not > understanding the code wrongly i40e and ixgbe check DD bit just for the > first descriptor in a group of 4, and they take all of them as used if the > first descriptor is used. > > By other hand, they do a "heavy" calculation when the descriptor ring wraps > which does not make sense (to me) if same performance goal is used. > > There are PMDs not supporting this option and I can not see any app or > example using it so I do not know how important is this function, its > accuracy and its performance impact. Can someone comment on this? > > Thanks I have version of this for virtio/vmxnet3 It is useful when using the interrupt control mode.