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? HPC proggies won't benefit from a partially filled pothole any
> > more that a ~zero ground clearance formula 1 car would. The 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 Don't the HPC guys just disable idle_balance(), or am I out of date again?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. I 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
