Re: [PATCH v13 09/13] sched/debug: Add migration stats due to non preferred CPUs

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

Hi Peter.

On 9/25/26 9:15 PM, Peter Zijlstra wrote:
> On Wed, Sep 09, 2026 at 07:26:13PM +0530, Shrikanth Hegde wrote:
>> Add a new stat,
>> - nr_migrations_cpu_non_preferred: number of migrations happened since
>>    a CPU was marked as non preferred due to high steal time.
>>
>> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
>> ---
>>   include/linux/sched.h | 1 +
>>   kernel/sched/core.c   | 9 +++++++--
>>   kernel/sched/debug.c  | 1 +
>>   3 files changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index d7cc77181ef9..48639b0c75d0 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -554,6 +554,7 @@ struct sched_statistics {
>>   	u64				nr_failed_migrations_running;
>>   	u64				nr_failed_migrations_hot;
>>   	u64				nr_forced_migrations;
>> +	u64				nr_migrations_cpu_non_preferred;
>>   
>>   	u64				nr_wakeups;
>>   	u64				nr_wakeups_sync;
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 458b8c6fd9af..fb8404bd47e2 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -11239,8 +11239,13 @@ static int sched_non_preferred_cpu_push_stop(void *arg)
>>   	context_unsafe_alias(rq);
>>   
>>   	if (task_rq(p) == rq && task_on_rq_queued(p) &&
>> -	    !is_migration_disabled(p))
>> -		rq = __migrate_task(rq, &rf, p, cpu);
>> +	    !is_migration_disabled(p)) {
>> +		struct rq *dest_rq = __migrate_task(rq, &rf, p, cpu);
>> +
>> +		if (rq != dest_rq)
>> +			schedstat_inc(p->stats.nr_migrations_cpu_non_preferred);
>> +		rq = dest_rq;
>> +	}
>>   
>>   	rq_unlock(rq, &rf);
>>   	raw_spin_unlock_irq(&p->pi_lock);
>> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
>> index fda10b3fa249..e6a3b516c703 100644
>> --- a/kernel/sched/debug.c
>> +++ b/kernel/sched/debug.c
>> @@ -1440,6 +1440,7 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
>>   		P_SCHEDSTAT(nr_failed_migrations_running);
>>   		P_SCHEDSTAT(nr_failed_migrations_hot);
>>   		P_SCHEDSTAT(nr_forced_migrations);
>> +		P_SCHEDSTAT(nr_migrations_cpu_non_preferred);
>>   		P_SCHEDSTAT(nr_wakeups);
>>   		P_SCHEDSTAT(nr_wakeups_sync);
>>   		P_SCHEDSTAT(nr_wakeups_migrate);
> 
> Should we not also bump the schedstat version? I forgot the rules, but
> you do change the output. And did we ever merge that perf schedstat
> thing, then that probably needs 'fixing' for the new format too.

This doesn't change /proc/schedstat. Tt does rather change in /proc/<pid>/sched
which isn't defined by version number IIRC.

Also i don't recollect that perf sched stat using anything from /proc/<pid>/sched

I skimmed through this.
https://lore.kernel.org/all/20260119175833.340369-1-swapnil.sapkal@amd.com/

So I don't think we need to update the version.