Re: [PATCH v3 09/20] sched/rt: Select a preferred CPU for wakeup and pulling rt task

[Shrikanth Hegde <sshegde@linux.ibm.com>]

Hi Peter.

On 6/9/26 5:00 PM, Shrikanth Hegde wrote:
> Hi Peter. Thanks for taking a look at the patches.
> 
> On 6/9/26 4:55 PM, Peter Zijlstra wrote:
>> On Thu, May 14, 2026 at 08:51:53PM +0530, Shrikanth Hegde wrote:
>>> For RT class,
>>> - During wakeup choose a preferred CPU.
>>> - For push_rt framework, limit pushing to preferred CPUs
>>> - Pull the rt task only if CPU is preferred.
>>
>> So this one might have the potential to break things. Preferring a
>> preferred cpu, sure, but to the exclusion of active, perhaps not.
>>
> 
> I don't think we are excluding active.
> 

I thought a bit more.
On most common workloads, rt is likely not dominant/significant in VM environments.

I am thinking to drop rt changes in the next version. If we see a need for it,
then that support could be added. I reverted these changes and ran real
life workload (daytrader) mentioned in the cover-letter and I don't see its
impact.

>> Also, where are the DL changes?
> 
> DL changes are not there. The reason being on such systems running DL 
> tasks will not make sense as timelines are subjected to vCPU preemption 
> and there is no easy way to force run a vCPU.
> 
> RT is not a primary use case too. But have seen a few workload spawn RT 
> tasks today. So it is there.
> 

So, initial support will be for FAIR only. Other class support could be brought
based on the use-case. Does that make sense?