linux-kernel - Re: [PATCH V3 2/3] tracing/osnoise: Add preempt/irq disable options

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Message-ID: <20221128153919.33c008d1@gandalf.local.home>
Date:   Mon, 28 Nov 2022 15:39:19 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Daniel Bristot de Oliveira <bristot@...nel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Juri Lelli <juri.lelli@...hat.com>,
        Clark Williams <williams@...hat.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 2/3] tracing/osnoise: Add preempt/irq disable options

On Fri, 25 Nov 2022 22:20:23 +0100
Daniel Bristot de Oliveira <bristot@...nel.org> wrote:

> @@ -1308,6 +1315,8 @@ static void notify_new_max_latency(u64 latency)
>   */
>  static int run_osnoise(void)
>  {
> +	bool preempt_disable = test_bit(OSN_PREEMPT_DISABLE, &osnoise_options);
> +	bool irq_disable = test_bit(OSN_IRQ_DISABLE, &osnoise_options);

	bool irq_disable = test_bit(OSN_IRQ_DISABLE, &osnoise_options);
	bool preempt_disable = IS_ENABLED(CONFIG_PREEMPT) &&
			!irq_disable && test_bit(OSN_PREEMPT_DISABLE, &osnoise_options);

>  	struct osnoise_variables *osn_var = this_cpu_osn_var();
>  	u64 start, sample, last_sample;
>  	u64 last_int_count, int_count;
> @@ -1335,6 +1344,14 @@ static int run_osnoise(void)
>  	 */
>  	threshold = tracing_thresh ? : 5000;
>  
> +	/*
> +	 * IRQ disable also implies in preempt disable.
> +	 */
> +	if (irq_disable)
> +		local_irq_disable();

	if (preempt_disable)
> +		preempt_disable();
> +
>  	/*
>  	 * Make sure NMIs see sampling first
>  	 */
> @@ -1422,16 +1439,21 @@ static int run_osnoise(void)
>  		 * cond_resched()
>  		 */
>  		if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
> -			local_irq_disable();
> +			if (!irq_disable)
> +				local_irq_disable();
> +
>  			rcu_momentary_dyntick_idle();
> -			local_irq_enable();
> +
> +			if (!irq_disable)
> +				local_irq_enable();
>  		}
>  
>  		/*
>  		 * For the non-preemptive kernel config: let threads runs, if
> -		 * they so wish.
> +		 * they so wish, unless set not do to so.
>  		 */
> -		cond_resched();
> +		if (!irq_disable && !preempt_disable)
> +			cond_resched();
>  
>  		last_sample = sample;
>  		last_int_count = int_count;
> @@ -1450,6 +1472,14 @@ static int run_osnoise(void)
>  	 */
>  	barrier();
>  
> +	/*
> +	 * Return to the preemptive state.
> +	 */

	if (preempt_disable)
> +		preempt_enable();
> +

> +	if (irq_disable)
> +		local_irq_enable();

-- Steve

>  	/*
>  	 * Save noise info.
>  	 */