linux-kernel - Re: [PATCH v3 2/3] sched/debug: dump domains' level

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Date: Thu, 4 Apr 2024 17:55:06 +0300
From: Vitalii Bursov <vitaly@...sov.com>
To: Valentin Schneider <vschneid@...hat.com>, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Daniel Bristot de Oliveira
 <bristot@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] sched/debug: dump domains' level



On 04.04.24 17:21, Valentin Schneider wrote:
> On 03/04/24 16:28, Vitalii Bursov wrote:
>> Knowing domain's level exactly can be useful when setting
>> relax_domain_level or cpuset.sched_relax_domain_level
>>
>> Usage:
>> cat /debug/sched/domains/cpu0/domain1/level
>> to dump cpu0 domain1's level.
>>
>> Signed-off-by: Vitalii Bursov <vitaly@...sov.com>
>> ---
>>  kernel/sched/debug.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
>> index 8d5d98a5834d..c1eb9a1afd13 100644
>> --- a/kernel/sched/debug.c
>> +++ b/kernel/sched/debug.c
>> @@ -425,6 +425,7 @@ static void register_sd(struct sched_domain *sd, struct dentry *parent)
>>
>>       debugfs_create_file("flags", 0444, parent, &sd->flags, &sd_flags_fops);
>>       debugfs_create_file("groups_flags", 0444, parent, &sd->groups->flags, &sd_flags_fops);
>> +	debugfs_create_u32("level", 0444, parent, (u32 *)&sd->level);
> 
> How about reusing the SDM macro? ->flags and ->groups_flags get special
> treatment for pretty printing, but the others don't need that.
> ---
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index c1eb9a1afd13e..f97902208b34d 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -419,13 +419,13 @@ static void register_sd(struct sched_domain *sd, struct dentry *parent)
>  	SDM(u32,   0644, busy_factor);
>  	SDM(u32,   0644, imbalance_pct);
>  	SDM(u32,   0644, cache_nice_tries);
> +	SDM(u32,   0444, level);
>  	SDM(str,   0444, name);
>  
>  #undef SDM
>  
>  	debugfs_create_file("flags", 0444, parent, &sd->flags, &sd_flags_fops);
>  	debugfs_create_file("groups_flags", 0444, parent, &sd->groups->flags, &sd_flags_fops);
> -	debugfs_create_u32("level", 0444, parent, (u32 *)&sd->level);
>  }
>  
>  void update_sched_domain_debugfs(void)
> 

This worked when I tried it. The reason why I chose an explicit implementation
with debugfs_create_u32() is because "level" is "int" and there's no
debugfs_create_{s32,int}(). While casting is not the best option either, it
hints that types mismatch.

In a few other cases when types do not match, casting is usually used. e.g.
mod_debug_add_ulong macro in kernel/module/stats.c:
#define mod_debug_add_ulong(name) debugfs_create_ulong(#name, 0400, mod_debugfs_root, (unsigned long *) &name.counter)
where "counter" can be s64 from the atomic64.

Thanks