linux-kernel - Re: [PATCH 08/10] psi: pressure stall information for CPU, memory, and IO

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Message-ID: <20180717142157.GF2494@hirez.programming.kicks-ass.net>
Date:   Tue, 17 Jul 2018 16:21:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vinayak Menon <vinmenon@...eaurora.org>,
        Christopher Lameter <cl@...ux.com>,
        Mike Galbraith <efault@....de>,
        Shakeel Butt <shakeelb@...gle.com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 08/10] psi: pressure stall information for CPU, memory,
 and IO

On Thu, Jul 12, 2018 at 01:29:40PM -0400, Johannes Weiner wrote:
> diff --git a/include/linux/sched/stat.h b/include/linux/sched/stat.h
> index 04f1321d14c4..ac39435d1521 100644
> --- a/include/linux/sched/stat.h
> +++ b/include/linux/sched/stat.h
> @@ -28,10 +28,14 @@ static inline int sched_info_on(void)
>  	return 1;
>  #elif defined(CONFIG_TASK_DELAY_ACCT)
>  	extern int delayacct_on;
> +	if (delayacct_on)
> +		return 1;
> +#elif defined(CONFIG_PSI)
> +	extern int psi_disabled;
> +	if (!psi_disabled)
> +		return 1;
>  #endif
> +	return 0;
>  }

Doesn't that want to be something like:

static inline bool sched_info_on(void)
{
#ifdef CONFIG_SCHEDSTAT
	return true;
#else /* !SCHEDSTAT */
#ifdef CONFIG_TASK_DELAY_ACCT
	extern int delayacct_on;
	if (delayacct_on)
		return true;
#endif /* DELAYACCT */
#ifdef CONFIG_PSI
	extern int psi_disabled;
	if (!psi_disabled)
		return true;
#endif
	return false;
#endif /* !SCHEDSTATE */
}

Such that if you build a TASK_DELAY_ACCT && PSI kernel, and boot with
nodelayacct, you still get sched_info_on().