linux-kernel - Re: [PATCH] sched: move access of avg_rt and avg

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Date: Fri, 22 Dec 2023 13:32:26 +0530
From: Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
To: Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...nel.org>
Cc: peterz@...radead.org, dietmar.eggemann@....com,
        linux-kernel@...r.kernel.org, srikar@...ux.vnet.ibm.com,
        yu.c.chen@...el.com, tim.c.chen@...ux.intel.com
Subject: Re: [PATCH] sched: move access of avg_rt and avg_dl into existing
 helper functions



On 12/21/23 9:46 PM, Vincent Guittot wrote:
> Hi Shrikanth,
> 
> On Wed, 20 Dec 2023 at 15:49, Shrikanth Hegde
> <sshegde@...ux.vnet.ibm.com> wrote:
>>
>>
>>
>> On 12/20/23 7:29 PM, Vincent Guittot wrote:
>>
>> Hi Vincent, thanks for taking a look.
>>
>>> On Wed, 20 Dec 2023 at 07:55, Shrikanth Hegde
>>> <sshegde@...ux.vnet.ibm.com> wrote:
>>>>
> 
> [...]
> 
>>>> -#ifdef CONFIG_HAVE_SCHED_AVG_IRQ
>>>> -       if (READ_ONCE(rq->avg_irq.util_avg))
>>>> +       if (cpu_util_irq(rq))
>>>
>>> cpu_util_irq doesn't call READ_ONCE()
>>>
>>
>>
>> I see. Actually it would be right if cpu_util_irq does call READ_ONCE no?
> 
> Yes, cpu_util_irq should call READ_ONCE()
> 

Ok. 

Sorry I forgot to mention about avg_irq. 
I will send out v2 with the above change of READ_ONCE added soon. 

>>
>> Sorry i havent yet understood the memory barriers in details. Please correct me
>> if i am wrong here,
>> since ___update_load_avg(&rq->avg_irq, 1) does use WRITE_ONCE and reading out this
>> value using cpu_util_irq on a different CPU should use READ_ONCE no?
> 
> Yes
> 
>>
>>>
>>>>                 return true;
>>>> -#endif
>>>>
>>>>         return false;
>>>>  }
>>>> @@ -9481,8 +9479,8 @@ static unsigned long scale_rt_capacity(int cpu)
>>>>          * avg_thermal.load_avg tracks thermal pressure and the weighted
>>>>          * average uses the actual delta max capacity(load).
>>>>          */
>>>> -       used = READ_ONCE(rq->avg_rt.util_avg);
>>>> -       used += READ_ONCE(rq->avg_dl.util_avg);
>>>> +       used = cpu_util_rt(rq);
>>>> +       used += cpu_util_dl(rq);
>>>>         used += thermal_load_avg(rq);
>>>>
>>>>         if (unlikely(used >= max))
>>>> --
>>>> 2.39.3
>>>>