From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <lcapitulino@redhat.com>
Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28])
 by dpdk.org (Postfix) with ESMTP id 8028D1B672
 for <dev@dpdk.org>; Fri, 10 Nov 2017 14:51:07 +0100 (CET)
Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com
 [10.5.11.13])
 (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by mx1.redhat.com (Postfix) with ESMTPS id BD17F61462;
 Fri, 10 Nov 2017 13:51:06 +0000 (UTC)
Received: from localhost (ovpn-116-155.phx2.redhat.com [10.3.116.155])
 by smtp.corp.redhat.com (Postfix) with ESMTP id 261E817A7A;
 Fri, 10 Nov 2017 13:51:03 +0000 (UTC)
Date: Fri, 10 Nov 2017 08:51:02 -0500
From: Luiz Capitulino <lcapitulino@redhat.com>
To: Bruce Richardson <bruce.richardson@intel.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>, "Ananyev, Konstantin"
 <konstantin.ananyev@intel.com>, Adrien Mazarguil
 <adrien.mazarguil@6wind.com>, Marcelo Tosatti <mtosatti@redhat.com>,
 "dev@dpdk.org" <dev@dpdk.org>
Message-ID: <20171110085102.4b86397a@redhat.com>
In-Reply-To: <20171110111451.GA9164@bricha3-MOBL3.ger.corp.intel.com>
References: <20171110060210.GA23340@amt.cnet>
 <20171110091219.GE24849@6wind.com>
 <2601191342CEEE43887BDE71AB9772585FABBC64@irsmsx105.ger.corp.intel.com>
 <ffb7ed09-e943-8a16-1be0-74e2ac3ce788@redhat.com>
 <20171110111451.GA9164@bricha3-MOBL3.ger.corp.intel.com>
Organization: Red Hat
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16
 (mx1.redhat.com [10.5.110.39]); Fri, 10 Nov 2017 13:51:06 +0000 (UTC)
Subject: Re: [dpdk-dev] [PATCH] testpmd: add nanosleep in main loop
X-BeenThere: dev@dpdk.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: DPDK patches and discussions <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: Fri, 10 Nov 2017 13:51:07 -0000

On Fri, 10 Nov 2017 11:14:51 +0000
Bruce Richardson <bruce.richardson@intel.com> 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.