Re: [PATCH v4 14/20] sched/core: Introduce a simple steal monitor

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

[...]

>>>>>>> This monitor is the one implementation out of quite many possible,
>>>>>>> right? I don't think it should live in the core scheduler files, it
>>>>>>> should be a module.
>>>>>
>>>>> I agree that this tight of an integration with the sched bits might not
>>>>> not be required.
>>>>>
>>>>>>
>>>>>> You mean similar to drivers/cpuidle/? a new one drivers/steal_monitor/ ?
>>>>>
>>>>> Since steal time is a virtualization concept, somewhere in drivers/virt/
>>>>> probably makes more sense unless we need some scheduler internal API to
>>>>> implement it which shouldn't be the case.
>>>>>
>>>>> All the driver has to do is track steal-time (which should be available
>>>>> via kcpustat_cpu_fetch()) periodically (using a workqueue?) and should
>>>>> do set_cpu_preferred() (which needs to be made available for other use
>>>>> cases anyways) so it should be possible.
>>>>
>>>> Yes. Seems like doable.
>>>>
>>>> Do you think it would make sense to keep the debugfs in sched still?
>>>
>>> The enable/disable part will be replaced with insmod/rmmod. The
>>> statistics part - IDK. It is nice to have all stats at the same
>>> place. On the other hand, without the driver loaded it would
>>> always read zeroes. It anyways is just a single line in sched/core.c,
>>> not a big deal.
>>>
>>
>> I was asking about these debugfs knobs.
>>
>> steal_monitor/high_threshold:500
>> steal_monitor/low_threshold:200
>> steal_monitor/sampling_period:1000
> 
> Those are the driver defaults. And if you want to override one, then:
> 
> insmod steal_monitor.ko high_threshold=400

ok.

I will try moving steal monitor into a driver.
- create a new one in drivers/virt named as steal_monitor
- enable/disable will be insmod/rmmod
- debug knobs will be module parameters.
- there will be default hooks, any arch needs specific handling it needs to do
   by adding its specific file. (somewhat close to cpuidle)


PS:
Sashiko too had some interesting comments for the series.
I have fixed a few.
https://sashiko.dev/#/patchset/20260617174139.155540-1-sshegde%40linux.ibm.com