From mboxrd@z Thu Jan 1 00:00:00 1970 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) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:organization :user-agent:in-reply-to:references:mime-version :content-transfer-encoding:content-type; bh=o8Yu5Jwf5eWjwEB1seopLwUY4wqTDHpjVqJSIvfq/+M=; b=We2fF/tvhnRXKx/nph07ApXsi2wLSl+yGHiZQaJDYVq4LzdZMp0wdyfdi2HpTgYlXP 8tvgKqg5gmYV0pxSS9oW/iHkMtofwWnVM2dd96dws5UhCMS1+UqKzZT/wUPXSEhRAYUq CXEZBH/Os1zEvzdvQyFMgmAB2F3Q1+yyKp5p0Wsqo+FvdDm/R43tFgFdVVkVDsOe6wbt fTNaPAE58dZmsKOIFfz9j6nxXbClf41LkPYELrLBF+azpjR4g4J/EzTOgR6BNwRaOTno P/Y+JbcQ239vKWEhpaJGXryfJLyIc6cksAjmetDbywD4NgS8+yh9W4S0ECDTmifQANt6 FHtQ== X-Gm-Message-State: ALoCoQn6v15EZ0vU8N1K1TjMF79sKjZ6Hib4MQZC1fu5lg9egApQdQUE2i6iKo40ajPG/m6Yiswy X-Received: by 10.194.236.66 with SMTP id us2mr69769572wjc.54.1432159359768; Wed, 20 May 2015 15:02:39 -0700 (PDT) Received: from xps13.localnet (2E6B6683.dsl.pool.telekom.hu. [46.107.102.131]) by mx.google.com with ESMTPSA id j12sm28903849wjn.48.2015.05.20.15.02.38 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 20 May 2015 15:02:38 -0700 (PDT) From: Thomas Monjalon To: Stephen Hemminger , "Dumitrescu, Cristian" Date: Thu, 21 May 2015 00:01:55 +0200 Message-ID: <1870211.3M6CNgV6Ua@xps13> Organization: 6WIND User-Agent: KMail/4.14.7 (Linux/4.0.1-1-ARCH; KDE/4.14.7; x86_64; ; ) In-Reply-To: <20150520105946.4ac86349@uryu.home.lan> 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-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Cc: dev@dpdk.org Subject: Re: [dpdk-dev] [PATCH v2] pipeline: add statistics for librte_pipeline ports and tables X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 20 May 2015 22:02:40 -0000 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).