linux-kernel - Re: [PATCH v5 2/3] sched/topology: Rework CPU capacity asymmetry detection

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Message-ID: <32ffee58-5ea9-1e01-c134-9fb90d1b1771@arm.com>
Date:   Thu, 3 Jun 2021 11:09:48 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Beata Michalska <beata.michalska@....com>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, corbet@....net, rdunlap@...radead.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v5 2/3] sched/topology: Rework CPU capacity asymmetry
 detection

On 02/06/2021 21:48, Beata Michalska wrote:
> On Wed, Jun 02, 2021 at 07:17:12PM +0200, Dietmar Eggemann wrote:
>> On 27/05/2021 19:07, Beata Michalska wrote:
>>> On Thu, May 27, 2021 at 05:08:42PM +0200, Dietmar Eggemann wrote:
>>>> On 26/05/2021 23:40, Beata Michalska wrote:
>>>>> On Wed, May 26, 2021 at 08:17:41PM +0200, Dietmar Eggemann wrote:
>>>>>> On 26/05/2021 14:51, Beata Michalska wrote:
>>>>>>> On Wed, May 26, 2021 at 01:15:46PM +0100, Beata Michalska wrote:
>>>>>>>> On Wed, May 26, 2021 at 11:52:25AM +0200, Dietmar Eggemann wrote:
>>>>>>>>> On 25/05/2021 12:29, Beata Michalska wrote:
>>>>>>>>>> On Tue, May 25, 2021 at 10:53:07AM +0100, Valentin Schneider wrote:
>>>>>>>>>>> On 24/05/21 23:55, Beata Michalska wrote:
>>>>>>>>>>>> On Mon, May 24, 2021 at 07:01:04PM +0100, Valentin Schneider wrote:
>>>>>>>>>>>>> On 24/05/21 11:16, Beata Michalska wrote:

[...]

> So what I have done is :
> 
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 77e6f79235ad..ec4ae225687e 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -1324,6 +1324,7 @@ asym_cpu_capacity_classify(struct sched_domain *sd,
>         if (!asym_cap_miss)
>                 sd_asym_flags |= SD_ASYM_CPUCAPACITY_FULL;
>  
> +       WARN_ONCE(cpu_smt_flags() & sd->flags, "Detected CPU capacity asymmetry on SMT level");
>  leave:
>         return sd_asym_flags;
>  }
> 
> Comment can be adjusted.
> This would sit in the classify function to nicely wrap asymmetry bits in one
> place. What do you think ?

... and you would need to pass in the sched domain pointer ;-)

Still prefer to check it in sd_init() since there is where we set the flags.

But you can't do 'cpu_smt_flags() & sd->flags'. MC level would hit too,
since it has SD_SHARE_PKG_RESOURCES as well.