linux-kernel - Re: [PATCH V3 4/9] tracing/hwlat: Implement the per-cpu mode

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Date:   Thu, 27 May 2021 14:29:13 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Phil Auld <pauld@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Kate Carcia <kcarcia@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Clark Willaims <williams@...hat.com>,
        John Kacur <jkacur@...hat.com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH V3 4/9] tracing/hwlat: Implement the per-cpu mode

On 5/27/21 1:58 PM, Juri Lelli wrote:
> Hi,
> 
> On 14/05/21 22:51, Daniel Bristot de Oliveira wrote:
> 
> [...]
> 
>> +/**
>> + * start_per_cpu_kthread - Kick off the hardware latency sampling/detector kthreads
>> + *
>> + * This starts the kernel threads that will sit on potentially all cpus and
>> + * sample the CPU timestamp counter (TSC or similar) and look for potential
>> + * hardware latencies.
>> + */
>> +static int start_per_cpu_kthreads(struct trace_array *tr)
>> +{
>> +	struct cpumask *current_mask = &save_cpumask;
>> +	struct cpumask *this_cpumask;
>> +	struct task_struct *kthread;
>> +	char comm[24];
>> +	int cpu;
>> +
>> +	if (!alloc_cpumask_var(&this_cpumask, GFP_KERNEL))
>> +		return -ENOMEM;
> 
> Is this_cpumask actually used anywhere?

OOpppsss, this is a left-over :-(....

Before starting using kthread_create_on_cpu(), I was using this_cpumask to set
the affinity of threads created via kthread_create().... but it is not needed
anymore.

I will remove it, good catch.

Thanks!
-- Daniel

> 
> Thanks,
> Juri
>