linux-kernel - Re: [PATCH v4 1/2] sched/fair: set rq->idle_stamp at the end of the sched_balance

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Message-ID: <5cde0f5b-b05f-4f89-a202-94b7a63a51b5@amperemail.onmicrosoft.com>
Date: Fri, 28 Nov 2025 21:01:24 +0800
From: Shijie Huang <shijie@...eremail.onmicrosoft.com>
To: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>,
 Huang Shijie <shijie@...amperecomputing.com>
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
 vincent.guittot@...aro.org, patches@...erecomputing.com, cl@...ux.com,
 Shubhang@...amperecomputing.com, dietmar.eggemann@....com,
 rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
 linux-kernel@...r.kernel.org, vschneid@...hat.com, kprateek.nayak@....com
Subject: Re: [PATCH v4 1/2] sched/fair: set rq->idle_stamp at the end of the
 sched_balance_newidle


On 28/11/2025 20:54, Shijie Huang wrote:
> On 28/11/2025 18:07, Madadi Vineeth Reddy wrote:
>>>        */
>>> -    this_rq->idle_stamp = rq_clock(this_rq);
>>> +    idle_stamp = rq_clock(this_rq);
>>> +
>>> +    this_rq->idle_stamp = 0;
>> IIUC, by setting this_rq->idle_stamp = 0 at the beginning, any call 
>> to update_rq_avg_idle() during
>> load balancing when tasks are pulled will fail the if 
>> (rq->idle_stamp) check, preventing the average
>> idle time from being updated.
>
>  1.) For the newidle balance, it is okay to prevent to update the 
> rq->avg_idle.
>
>  2.) For the idle balance, the this_rq->idle_stamp is not zero, and it 
> can update the rq->avg_idle.
>
>             Can the idle balance and newidle balance run at the same 
> time?

I mean on the same CPU.


>
>
>  3.) For the busy balance, the  this_rq->idle_stamp should be zero, no 
> need to update the rq->avg_idle.
>