linux-kernel - Re: [RFC PATCH 03/23] sched/core: Initialize the class of a new task

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Message-ID: <YzG92YDyBK/0W+5u@google.com>
Date:   Mon, 26 Sep 2022 14:57:29 +0000
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ricardo Neri <ricardo.neri@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, "Tim C . Chen" <tim.c.chen@...el.com>
Subject: Re: [RFC PATCH 03/23] sched/core: Initialize the class of a new task

Hi Ricardo,

On Fri, Sep 09, 2022 at 04:11:45PM -0700, Ricardo Neri wrote:
> New tasks shall start life as unclassified. They will be classified by
> hardware when they run.
> 
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Tim C. Chen <tim.c.chen@...el.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: x86@...nel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> ---
>  kernel/sched/core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index ee28253c9ac0..db548c1a25ef 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4336,6 +4336,9 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
>  	p->se.prev_sum_exec_runtime	= 0;
>  	p->se.nr_migrations		= 0;
>  	p->se.vruntime			= 0;
> +#ifdef CONFIG_SCHED_TASK_CLASSES
> +	p->class			= TASK_CLASS_UNCLASSIFIED;
> +#endif

I find the term 'class' very broad and unclear what kind of class (without
further reading). So I am worried about how this generic term usage plays
with Linux source code in the long-term (like what if someone else comes up
with a usage of term 'class' that is unrelated to IPC.)

To that end, I was wondering if it could be renamed to p->ipc_class, and
CONFIG_SCHED_TASK_IPC_CLASSES, or something.

thanks,

 - Joel



>  	INIT_LIST_HEAD(&p->se.group_node);
>  
>  #ifdef CONFIG_FAIR_GROUP_SCHED
> -- 
> 2.25.1
>