From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: <cristian.dumitrescu@intel.com> Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by dpdk.org (Postfix) with ESMTP id 3EC3A5A0A for <dev@dpdk.org>; Thu, 21 May 2015 01:56:57 +0200 (CEST) Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga101.fm.intel.com with ESMTP; 20 May 2015 16:56:55 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.13,466,1427785200"; d="scan'208";a="729315033" Received: from irsmsx110.ger.corp.intel.com ([163.33.3.25]) by fmsmga002.fm.intel.com with ESMTP; 20 May 2015 16:56:53 -0700 Received: from irsmsx108.ger.corp.intel.com ([169.254.11.59]) by irsmsx110.ger.corp.intel.com ([163.33.3.25]) with mapi id 14.03.0224.002; Thu, 21 May 2015 00:56:52 +0100 From: "Dumitrescu, Cristian" <cristian.dumitrescu@intel.com> To: Thomas Monjalon <thomas.monjalon@6wind.com>, Stephen Hemminger <stephen@networkplumber.org> Thread-Topic: [dpdk-dev] [PATCH v2] pipeline: add statistics for librte_pipeline ports and tables Thread-Index: AQHQkWZQUPiGW1BlN0muPEnhvuILX52D/wVsgADlY3D///8CgIAANokAgABDp4CAACzawA== Date: Wed, 20 May 2015 23:56:52 +0000 Message-ID: <3EB4FA525960D640B5BDFFD6A3D891263236A970@IRSMSX108.ger.corp.intel.com> References: <1430396143-10936-1-git-send-email-michalx.k.jastrzebski@intel.com> <2017641.P0ts6fjbPO@xps13> <20150520105946.4ac86349@uryu.home.lan> <1870211.3M6CNgV6Ua@xps13> In-Reply-To: <1870211.3M6CNgV6Ua@xps13> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [163.33.239.182] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Cc: "dev@dpdk.org" <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 <dev.dpdk.org> List-Unsubscribe: <http://dpdk.org/ml/options/dev>, <mailto:dev-request@dpdk.org?subject=unsubscribe> List-Archive: <http://dpdk.org/ml/archives/dev/> List-Post: <mailto:dev@dpdk.org> List-Help: <mailto:dev-request@dpdk.org?subject=help> List-Subscribe: <http://dpdk.org/ml/listinfo/dev>, <mailto:dev-request@dpdk.org?subject=subscribe> X-List-Received-Date: Wed, 20 May 2015 23:56:58 -0000 > -----Original Message----- > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com] > Sent: Wednesday, May 20, 2015 11:02 PM > To: Stephen Hemminger; Dumitrescu, Cristian > Cc: dev@dpdk.org > Subject: Re: [dpdk-dev] [PATCH v2] pipeline: add statistics for librte_pi= peline > ports and tables >=20 > 2015-05-20 10:59, Stephen Hemminger: > > On Wed, 20 May 2015 16:44:35 +0200 > > Thomas Monjalon <thomas.monjalon@6wind.com> 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 givi= ng 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 dat= a > > > > > > structures and functions are not changed by the build time opti= on. > > > > > > > > > > > > But what can you do for statistics? We all know that collecting= the > stats > > > > > > sucks up CPU cycles, especially due to memory accesses, so stat= s > always > > > > > > have a run-time cost. Traditionally, stats are typically enable= d for > > > > > > debugging purposes and then turned off for the release version > when > > > > > > performance is required. How can this be done if build time fla= gs are > not > > > > > > used? > > > > > > > > > > Statistics in drivers are always enabled (first solution). > > > > > If those statistics are only used for debugging, why not using th= e > build-time > > > > > option CONFIG_RTE_LOG_LEVEL? (second solution) > > > > > > > > Can you please describe what solution 2 on your list (build-time lo= g > > > > level) consists of? > > > > > > > > I see log level useful for printing messages when an event takes pl= ace, > > > > 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 t= he > > > > value of those counters is 0; when the build-time is on, then the s= tats > > > > 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 =3D=3D 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 >=20 > Yes. Maybe that having a benchmark with per-cpu stats would help to discu= ss > the first solution (stats always enabled). What are per-cpu stats? Are you referring to the false sharing problem when= each cpu core maintains its own stats, but stats from several cores end up= being stores in the same cache line? We don't have this problem here.