From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by inbox.dpdk.org (Postfix) with ESMTP id AF707A04C0; Thu, 14 Nov 2019 10:57:55 +0100 (CET) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id B050B2BAE; Thu, 14 Nov 2019 10:57:54 +0100 (CET) Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by dpdk.org (Postfix) with ESMTP id F00AF2B86; Thu, 14 Nov 2019 10:57:51 +0100 (CET) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Nov 2019 01:57:50 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.68,304,1569308400"; d="scan'208";a="203021139" Received: from aburakov-mobl1.ger.corp.intel.com (HELO [10.252.7.220]) ([10.252.7.220]) by fmsmga008.fm.intel.com with ESMTP; 14 Nov 2019 01:57:48 -0800 To: Venumadhav Josyula Cc: Bruce Richardson , users@dpdk.org, dev@dpdk.org, Venumadhav Josyula References: <20191113091927.GA1501@bricha3-MOBL.ger.corp.intel.com> <70f4e9f0-70f7-aa4a-6c5d-c24308d196c2@intel.com> <3c014e01-3635-df19-a11c-2db09b03d423@intel.com> From: "Burakov, Anatoly" Message-ID: Date: Thu, 14 Nov 2019 09:57:48 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: Re: [dpdk-dev] time taken for allocation of mempool. 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 14-Nov-19 9:50 AM, Venumadhav Josyula wrote: > Hi Anatoly, > > Thanks for quick response. We want to understand, if there will be > performance implications because of iova-mode being va. We want to > understand,  specifically in terms following > > * cache misses > * Branch misses etc > * translation of va addr -> phy addr when packet is receieved > There will be no impact whatsoever. You mentioned that you were already using VFIO, so you were already making use of IOMMU*. Cache/branch misses are independent of IOVA layout, and translations are done by the hardware (in either IOVA as PA or IOVA as VA case - IOMMU doesn't care what you program it with, it still does the translation, even if it's a 1:1 IOVA-to-PA mapping), so there is nothing that can cause degradation. In fact, under some circumstances, using IOVA as VA mode can be used to get performance /gains/, because the code can take advantage of the fact that there are large IOVA-contiguous segments and no page-by-page allocations. Some drivers (IIRC octeontx mempool?) even refuse to work in IOVA as PA mode due to huge overheads of page-by-page buffer offset tracking. TL;DR you'll be fine :) * Using an IOMMU can /theoretically/ affect performance due to hardware IOVA->PA translation and IOTLB cache misses. In practice, i have never been able to observe /any/ effect whatsoever on performance when using IOMMU vs. without using IOMMU, so this appears to not be a concern /in practice/. >  Thanks and regards > Venu > > On Thu, 14 Nov 2019 at 15:14, Burakov, Anatoly > > wrote: > > On 13-Nov-19 9:01 PM, Venumadhav Josyula wrote: > > Hi Anatoly, > > > > By default w/o specifying --iova-mode option is iova-mode=pa by > default ? > > > > Thanks > > Venu > > > > In 18.11, there is a very specific set of circumstances that will > default to IOVA as VA mode. Future releases have become more > aggressive, > to the point of IOVA as VA mode being the default unless asked > otherwise. So yes, it is highly likely that in your case, IOVA as PA is > picked as the default. > > -- > Thanks, > Anatoly > -- Thanks, Anatoly