linux-kernel - Re: [RFC PATCH] preempt: Add a generic function to return the preemption string.

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Message-ID: <20250109114339.GB2981@noisy.programming.kicks-ass.net>
Date: Thu, 9 Jan 2025 12:43:39 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
	Ben Segall <bsegall@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	Mel Gorman <mgorman@...e.de>, Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Will Deacon <will@...nel.org>, x86@...nel.org
Subject: Re: [RFC PATCH] preempt: Add a generic function to return the
 preemption string.

On Fri, Dec 06, 2024 at 12:34:31PM +0100, Sebastian Andrzej Siewior wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 95e40895a5190..8f5517dbe07d4 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7642,6 +7642,30 @@ static inline void preempt_dynamic_init(void) { }
>  
>  #endif /* CONFIG_PREEMPT_DYNAMIC */
>  
> +const char *preempt_model_str(void)
> +{
> +	if (IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY) && preempt_model_lazy()) {
> +		if (preempt_model_rt())
> +			return "PREEMPT_RT+LAZY";
> +		if (preempt_model_full())
> +			return "PREEMPT+LAZY";
> +		if (preempt_model_voluntary())
> +			return "VOLUNTARY+LAZY";
> +		if (preempt_model_none())
> +			return "NONE+LAZY";
> +	} else {
> +		if (preempt_model_rt())
> +			return "PREEMPT_RT";
> +		if (preempt_model_full())
> +			return "PREEMPT";
> +		if (preempt_model_voluntary())
> +			return "VOLUNTARY";
> +		if (preempt_model_none())
> +			return "NONE";
> +	}
> +	return "UNKNOWN-PREEMPT";
> +}

Hurmph.. a bunch of those combinations are nonsense :/

Also, we have a string thing in sched_dynamic_show().

Can't we do something like:

const char *preempt_model_str(void)
{
	static char buf[128];
	size_t off = 0, len = sizeof(buf), r;
	bool brace = IS_ENABLED(CONFIG_PREEMPT_RT) &&
		     (IS_ENABLED(CONFIG_PREEMPT_DYNAMIC) ||
		      IS_ENABLED(CONFIG_PREEMPT_LAZY));

	if (IS_ENABLED(CONFIG_PREEMPT_BUILD)) {
		r = snprintf(buf + off, len, "PREEMPT");
		off += r;
		len -= r;

		if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
			r = snprintf(buf + off, len, "%sRT%s", 
					brace ? "_{" : "_",
					brace ? "," : "");
			off += r;
			len -= r;
		}

		if (IS_ENABLED(CONFIG_PREEMPT_DYNAMIC)) {
			snprintf(buf + off, len, "(%s)%s", 
				preempt_modes[preempt_dynamic_mode],
				brace ? "}" : "");
			retun buf;
		}

		if (IS_ENABLED(CONFIG_PREEMPT_LAZY)) {
			snprintf(buf + off, len, "LAZY%s", 
				brace ? "}" : "");
			retun buf;
		}

		return buf;
	}

	if (IS_ENABLED(CONFIG_VOLUNTARY_BUILD))
		return "VOLUNTARY";

	return "NONE";
}