Re: [RFC PATCH 7/9] housekeeping: Use own boot option, independant from nohz

[Mike Galbraith]

On Tue, 2017-08-15 at 08:30 -0700, Paul E. McKenney wrote:
> On Tue, Aug 15, 2017 at 05:15:23PM +0200, Mike Galbraith wrote:
> > On Tue, 2017-08-15 at 15:07 +0200, Frederic Weisbecker wrote:
> > > On Mon, Aug 14, 2017 at 08:29:46PM +0200, Mike Galbraith wrote:
> > > > On Mon, 2017-08-14 at 13:34 -0400, Luiz Capitulino wrote:
> > > > > On Mon, 14 Aug 2017 19:01:09 +0200
> > > > > 
> > > > > > What is the source of the load balancing inducing such latency when a single
> > > > > > task is affine to a CPU? If this is idle load balancing, it is now affine to
> > > > > > housekeepers. If this is task wakeup then it's suprising because select_task_rq()
> > > > > > is optimized toward single CPU affinity.
> > > > > 
> > > > > I guess it was idle load balancing, but I don't remember because this
> > > > > was a few years ago. I think this might be reproducible without using
> > > > > isolcpus=. I'll give it a try shortly and let you know.
> > > > 
> > > > idle_balance() can swamp other noise by a couple orders of magnitude,
> > > 
> > > Ah I missed that one. Is there any way we can also lower the overhead there?
> > 
> > Why? ÂHPC proggies won't benefit from a partially filled pothole any
> > more that a ~zero ground clearance formula 1 car would. ÂThe pothole
> > intolerant either isolate, killing (most) LB, or they meet a wall.
> 
> Don't the HPC guys just disable idle_balance(), or am I out of date again?

They could do just that if what they're doing is not really critical. 
I'm not an HPC guy, so can only speculate. ÂI don't see much difference
between HPC and RT though, the rules of the game seem to be about the
same (them both being HPC;).. what you can control, you do control.

	-Mike