Re: [dpdk-dev] [PATCH] testpmd: add nanosleep in main loop

[Luiz Capitulino <lcapitulino@redhat.com>]

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.