From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Monjalon Subject: Re: [PATCH v2] pipeline: add statistics for librte_pipeline ports and tables Date: Wed, 20 May 2015 16:44:35 +0200 Message-ID: <2017641.P0ts6fjbPO@xps13> References: <1430396143-10936-1-git-send-email-michalx.k.jastrzebski@intel.com> <43396928.Zqf8pLaHBD@xps13> <3EB4FA525960D640B5BDFFD6A3D891263236A65D@IRSMSX108.ger.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: dev@dpdk.org To: "Dumitrescu, Cristian" Return-path: Received: from mail-wi0-f172.google.com (mail-wi0-f172.google.com [209.85.212.172]) by dpdk.org (Postfix) with ESMTP id 49CDBC320 for ; Wed, 20 May 2015 16:45:21 +0200 (CEST) Received: by wicmc15 with SMTP id mc15so152214785wic.1 for ; Wed, 20 May 2015 07:45:21 -0700 (PDT) In-Reply-To: <3EB4FA525960D640B5BDFFD6A3D891263236A65D@IRSMSX108.ger.corp.intel.com> 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" Please Cristian, do not top post. I'm replacing your comment in the right context. 2015-05-20 13:57, Dumitrescu, Cristian: > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com] > > Thanks for the detailed explanation. > > > > You are raising a trade-off problem about > > feature/maintenance/performance. > > I think we must choose among 4 solutions: > > 1/ always enabled > > 2/ build-time log level > > 3/ run-time option > > 4/ build-time option > > > > It's good to have this discussion and let other contributors giving their > > opinion. > > > > 2015-05-19 22:41, Dumitrescu, Cristian: > > > 1. What is the technical solution to avoid performance loss due to stats > > > support? > > > Generally, I would agree with you that config options should be avoided, > > > especially those that alter the API (function prototypes, data structure > > > layouts, etc). Please note this is not the case for any of our patches, > > > as only the stats collection is enabled/disabled, while the data > > > structures and functions are not changed by the build time option. > > > > > > But what can you do for statistics? We all know that collecting the stats > > > sucks up CPU cycles, especially due to memory accesses, so stats always > > > have a run-time cost. Traditionally, stats are typically enabled for > > > debugging purposes and then turned off for the release version when > > > performance is required. How can this be done if build time flags are not > > > used? > > > > Statistics in drivers are always enabled (first solution). > > If those statistics are only used for debugging, why not using the build-time > > option CONFIG_RTE_LOG_LEVEL? (second solution) > > Can you please describe what solution 2 on your list (build-time log > level) consists of? > > I see log level useful for printing messages when an event takes place, > but this is not what these stats patches are about. We want to poll > for those counters on demand: if the build-time flag is off, then the > value of those counters is 0; when the build-time is on, then the stats > counters have the real value. Basically, the build-time flag only > enables/disables the update of the counters at run-time, which is where > CPU cycles are consumed. I am not sure how the log levels can help here? I think that counting stats is a kind of logging. Some stats are always counted (see drivers) and you want to use these ones only for debugging (after rebuilding DPDK with some debug options). So I suggest, as second solution, to check CONFIG_RTE_LOG_LEVEL is at debug level instead of having one option per module. It would be implemented with "#if RTE_LOG_LEVEL == RTE_LOG_DEBUG" in RTE_PIPELINE_STATS_ADD.