Re: [RFC PATCH 0/2] Adjust CFS loadbalance to adapt QEMU CPU topology.

[Peter Zijlstra]

On Mon, Jul 24, 2023 at 02:57:57PM +0800, luoben@xxxxxxxxxxxxxxxxx wrote:

> > Right, why is this a problem? Hyperthreads are supposed to be symmetric,
> > it doesn't matter which of the two are active, the important thing is to
> > only have one active if we can.
> > 
> > (Unlike Power7, they have asymmetric SMT)
> > 
> 
> hi Peter and Vincent,
> 
> Some upper-level monitoring logic may take the CPU usage as a metric for
> computing resource scaling. Imbalanced scheduling can create the illusion
> of CPU resource scarcity, leading to more frequent triggering of resource
> expansion by the upper-level scheduling system. However, this is actually
> a waste of resources. So, we think this may be a problem.

This is a problem of your monitoring logic -- there is absolutely no
functional problem with the kernel AFAICT.

Teach the thing about SMT instead.

> Could you please take a further look at PATCH#2? We found that the default
> 'nr' value did not perform well under our scenario, and we believe that
> adjustable variables would be more appropriate.

That patch is tweaking default disabled code -- which we should be
removing sometime soon I suppose. So no.