From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH] testpmd: add nanosleep in main loop Date: Sat, 11 Nov 2017 02:01:13 -0200 Message-ID: <20171111040113.GE23577@amt.cnet> References: <20171110060210.GA23340@amt.cnet> <20171110091219.GE24849@6wind.com> <2601191342CEEE43887BDE71AB9772585FABBC64@irsmsx105.ger.corp.intel.com> <20171110111451.GA9164@bricha3-MOBL3.ger.corp.intel.com> <20171110085102.4b86397a@redhat.com> <20171111035921.GD23577@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Bruce Richardson , Daniel Bristot de Oliveira , "Ananyev, Konstantin" , Adrien Mazarguil , "dev@dpdk.org" To: Luiz Capitulino Return-path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id D95DA1B20E for ; Sat, 11 Nov 2017 17:14:54 +0100 (CET) Content-Disposition: inline In-Reply-To: <20171111035921.GD23577@amt.cnet> 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 Sat, Nov 11, 2017 at 01:59:21AM -0200, Marcelo Tosatti wrote: > On Fri, Nov 10, 2017 at 08:51:02AM -0500, Luiz Capitulino wrote: > > On Fri, 10 Nov 2017 11:14:51 +0000 > > Bruce Richardson wrote: > > > > > On Fri, Nov 10, 2017 at 11:42:56AM +0100, Daniel Bristot de Oliveira wrote: > > > > > > > > > > > > On 11/10/2017 11:14 AM, Ananyev, Konstantin wrote: > > > > > Agree with Adrian here - the patch doesn't fix the problem in any case, > > > > > > > > I would agree with you if it were possible to assume one can fully > > > > isolate a CPU on Linux... but it is not... > > > > > > > > This: > > > > https://lwn.net/Articles/659490/ > > > > > > > > is still an open issue, and the reason why it is an open issue is the > > > > kernel threads that need to run on every CPU, mainly when using the > > > > PREEMPT_RT, which turns almost everything on threads. > > > > > > > > > while introducing an unnecessary slowdown in testpmd iofwd mode. > > > > > Please think up some other approach. > > > > > > > > The other approach is to increase the priority of all other threads that > > > > run on the isolate CPU. But that is not a good idea at all, as the other > > > > threads might preempt the busy-loop thread at the worst possible moment. > > > > > > > > Using the knowledge of the thread about when it is the best time to give > > > > a chance for other threads to run would be a smarter decision. > > > > > > > I don't like having this in the main loop either, and to echo others I > > > wouldn't have thought that testpmd was actually used as anything other > > > than a testing app. > > > > That's why we're patching it. We want to be aware of the implications. > > If it's not good for testpmd, it may not be good for production either. > > The arguments raised so far against the patch have been: > > 1) Performance is reduced. > Reply: > * Of course performance is reduced, but any solution will also > reduce performance similary. > * Performance is reduced but within the acceptable limits set by > NFV standards. So the performance reduction argument is kind > of not an issue (in my POV). > > 2) Testpmd is a test application. > > Well, if one would like to avoid XFS corruption or other similar > results caused by the not possibility of running poll mode testpmd > (while testing) then he should enable the options (which are disabled > by default). Moreover, testpmd is an example application used by > production developers, so it should be integrated to testpmd. > > > Does anyone have arguments against the reasoning above ? Note: yes the kernel seems to be the proper place to fix this, however: 1) It'll take some time to fix the kernel to handle the problem. 2) In the meantime, a temporary workaround in DPDK is available.