linux-kernel - Re: [PATCH V4 2/3] tracing/osnoise: Add preempt and/or irq disabled options

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Message-ID: <20221209153552.4c7099cd@gandalf.local.home>
Date:   Fri, 9 Dec 2022 15:35:52 -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>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 2/3] tracing/osnoise: Add preempt and/or irq disabled
 options

On Wed, 30 Nov 2022 19:19:10 +0100
Daniel Bristot de Oliveira <bristot@...nel.org> wrote:


Hi Daniel,

As I was adding this series, I noticed an issue that needs to be fixed.

>  static int run_osnoise(void)
>  {
> +	bool irq_disable = test_bit(OSN_IRQ_DISABLE, &osnoise_options);
>  	struct osnoise_variables *osn_var = this_cpu_osn_var();
>  	u64 start, sample, last_sample;
>  	u64 last_int_count, int_count;
> @@ -1315,11 +1323,18 @@ static int run_osnoise(void)
>  	s64 total, last_total = 0;
>  	struct osnoise_sample s;
>  	unsigned int threshold;
> +	bool preempt_disable;

Let's use a different name for the above variable.

>  	u64 runtime, stop_in;
>  	u64 sum_noise = 0;
>  	int hw_count = 0;
>  	int ret = -1;
>  
> +	/*
> +	 * Disabling preemption is only required if IRQs are enabled,
> +	 * and the options is set on.
> +	 */
> +	preempt_disable = !irq_disable && test_bit(OSN_PREEMPT_DISABLE, &osnoise_options);
> +
>  	/*
>  	 * Considers the current thread as the workload.
>  	 */
> @@ -1335,6 +1350,15 @@ static int run_osnoise(void)
>  	 */
>  	threshold = tracing_thresh ? : 5000;
>  
> +	/*
> +	 * Apply PREEMPT and IRQ disabled options.
> +	 */
> +	if (irq_disable)
> +		local_irq_disable();
> +
> +	if (preempt_disable)
> +		preempt_disable();
> +

The only reason the above works is because preempt_disable() is a macro.
If it was a function, then it would likely fail to build (as you are
overriding the name with a bool variable).

-- Steve