Re: [PATCH] sched: Skip useless sched_balance_running acquisition if load balance is not due

[K Prateek Nayak]

Hello Peter,

On 4/18/2025 2:58 PM, Peter Zijlstra wrote:
> On Fri, Apr 18, 2025 at 10:56:04AM +0530, K Prateek Nayak wrote:
> > Hello Peter,
> >
> > On 4/17/2025 5:31 PM, Peter Zijlstra wrote:
> > > > o Since this is a single flag across the entire system, it also implies
> > > >     CPUs cannon concurrently do load balancing across different NUMA
> > > >     domains which seems reasonable since a load balance at lower NUMA
> > > >     domain can potentially change the "nr_numa_running" and
> > > >     "nr_preferred_running" stats for the higher domain but if this is the
> > > >     case, a newidle balance at lower NUMA domain can interfere with a
> > > >     concurrent busy / newidle load balancing at higher NUMA domain.
> > > >     Is this expected? Should newidle balance be serialized too?
> > >
> > > Serializing new-idle might create too much idle time.
> >
> > In the context of busy and idle balancing, What are your thoughts on a
> > per sd "serialize' flag?
>
> My sekret hope is that this push stuff can rid us all the idle balance
> bits. But yeah, early days on that.
>
> Other than that, I don't quite see why we should split that, busy
> balancing is the one that runs more often and is the one that should be
> serialized to avoid too much cross node traffic and all that, no?
>
> The idle thing is less often, why not limit that?

Makes sense. I'll add it to the set of my weekend experiment runs.

--
Thanks and Regards,
Prateek