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: Thu, 21 May 2015 00:01:55 +0200 Message-ID: <1870211.3M6CNgV6Ua@xps13> References: <1430396143-10936-1-git-send-email-michalx.k.jastrzebski@intel.com> <2017641.P0ts6fjbPO@xps13> <20150520105946.4ac86349@uryu.home.lan> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: dev@dpdk.org To: Stephen Hemminger , "Dumitrescu, Cristian" Return-path: Received: from mail-wi0-f177.google.com (mail-wi0-f177.google.com [209.85.212.177]) by dpdk.org (Postfix) with ESMTP id DA2BA5A4F for ; Thu, 21 May 2015 00:02:39 +0200 (CEST) Received: by wizk4 with SMTP id k4so170367893wiz.1 for ; Wed, 20 May 2015 15:02:39 -0700 (PDT) In-Reply-To: <20150520105946.4ac86349@uryu.home.lan> 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" 2015-05-20 10:59, Stephen Hemminger: > On Wed, 20 May 2015 16:44:35 +0200 > Thomas Monjalon wrote: > > > 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. > > > > In my experience, per-queue or per-cpu statistics have no visible performance > impact. And every real world deployment wants statistics Yes. Maybe that having a benchmark with per-cpu stats would help to discuss the first solution (stats always enabled).