linux-kernel - Re: [PATCH V4 01/19] trace/osnoise: Do not follow tracing

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Date:   Fri, 22 Oct 2021 22:23:01 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Daniel Bristot de Oliveira <bristot@...nel.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Tom Zanussi <zanussi@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Clark Williams <williams@...hat.com>,
        John Kacur <jkacur@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-rt-users@...r.kernel.org, linux-trace-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 01/19] trace/osnoise: Do not follow tracing_cpumask

On Thu, 21 Oct 2021 14:56:39 +0200
Daniel Bristot de Oliveira <bristot@...nel.org> wrote:

> In preparation to support multiple instances, decople the

    "decouple"

> osnoise/timelat workload from instance specific tracing_cpumask.
> 
> Different instances can have conflicing cpumasks, making osnoise

   "conflicting"

May I suggest a spell check for your commit logs? ;-)

> workload management needlessly complex. Osnoise already have its
> global cpu mask.
> 
> I also thought about using the first instance mask, but the
> "first" instance could be removed before the others.
> 
> This also fixes the problem that changing the tracing_mask was not
> re-starting the trace.
> 
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Tom Zanussi <zanussi@...nel.org>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: Clark Williams <williams@...hat.com>
> Cc: John Kacur <jkacur@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Cc: Daniel Bristot de Oliveira <bristot@...nel.org>
> Cc: linux-rt-users@...r.kernel.org
> Cc: linux-trace-devel@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Daniel Bristot de Oliveira <bristot@...nel.org>
> ---
>  kernel/trace/trace_osnoise.c | 25 +++++++------------------
>  1 file changed, 7 insertions(+), 18 deletions(-)
> 
> diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
> index ce053619f289..7b1f8187764c 100644
> --- a/kernel/trace/trace_osnoise.c
> +++ b/kernel/trace/trace_osnoise.c
> @@ -1553,13 +1553,10 @@ static int start_per_cpu_kthreads(struct trace_array *tr)
>  
>  	cpus_read_lock();
>  	/*
> -	 * Run only on CPUs in which trace and osnoise are allowed to run.
> +	 * Run only on online CPUs in which trace and osnoise are allowed to

  which trace and osnise? I thought we were removing "trace"?

-- Steve

> +	 * run.
>  	 */
> -	cpumask_and(current_mask, tr->tracing_cpumask, &osnoise_cpumask);
> -	/*
> -	 * And the CPU is online.
> -	 */
> -	cpumask_and(current_mask, cpu_online_mask, current_mask);
> +	cpumask_and(current_mask, cpu_online_mask, &osnoise_cpumask);
>  
>  	for_each_possible_cpu(cpu)
>  		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
> @@ -1580,10 +1577,8 @@ static int start_per_cpu_kthreads(struct trace_array *tr)
>  #ifdef CONFIG_HOTPLUG_CPU
>  static void osnoise_hotplug_workfn(struct work_struct *dummy)
>  {
> -	struct trace_array *tr = osnoise_trace;
>  	unsigned int cpu = smp_processor_id();
>  
> -
>  	mutex_lock(&trace_types_lock);
>  
>  	if (!osnoise_busy)
> @@ -1595,9 +1590,6 @@ static void osnoise_hotplug_workfn(struct work_struct *dummy)
>  	if (!cpumask_test_cpu(cpu, &osnoise_cpumask))
>  		goto out_unlock;
>  
> -	if (!cpumask_test_cpu(cpu, tr->tracing_cpumask))
> -		goto out_unlock;
> -
>  	start_kthread(cpu);
>  
>  out_unlock:
> @@ -1700,13 +1692,10 @@ static void osnoise_tracer_stop(struct trace_array *tr);
>   * interface to the osnoise trace. By default, it lists all  CPUs,
>   * in this way, allowing osnoise threads to run on any online CPU
>   * of the system. It serves to restrict the execution of osnoise to the
> - * set of CPUs writing via this interface. Note that osnoise also
> - * respects the "tracing_cpumask." Hence, osnoise threads will run only
> - * on the set of CPUs allowed here AND on "tracing_cpumask." Why not
> - * have just "tracing_cpumask?" Because the user might be interested
> - * in tracing what is running on other CPUs. For instance, one might
> - * run osnoise in one HT CPU while observing what is running on the
> - * sibling HT CPU.
> + * set of CPUs writing via this interface. Why not use "tracing_cpumask"?
> + * Because the user might be interested in tracing what is running on
> + * other CPUs. For instance, one might run osnoise in one HT CPU
> + * while observing what is running on the sibling HT CPU.
>   */
>  static ssize_t
>  osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,