linux-kernel - Re: [PATCH v0 14/71] perf tools: Add cpu to struct thread

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Message-ID: <20131211141908.GC1458@ghostprotocols.net>
Date:	Wed, 11 Dec 2013 11:19:08 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH v0 14/71] perf tools: Add cpu to struct thread

Em Wed, Dec 11, 2013 at 02:36:26PM +0200, Alexander Shishkin escreveu:
> From: Adrian Hunter <adrian.hunter@...el.com>
> 
> Tools may wish to track on which cpu a thread
> is running.  Add 'cpu' to struct thread for
> that purpose.  Also add machine functions to
> get / set the cpu for a tid.
> 
> This will be used to determine the cpu when
> decoding a per-thread Instruction Trace.
> 
> 
> +++ b/tools/perf/util/machine.c
> @@ -1412,3 +1412,29 @@ pid_t machine__get_thread_pid(struct machine *machine, pid_t tid)
>  
>  	return thread->pid_;
>  }
> +
> +int machine__get_thread_cpu(struct machine *machine, pid_t tid, pid_t *pid)
> +{
> +	struct thread *thread = machine__find_thread(machine, tid);
> +
> +	if (!thread)
> +		return -1;
> +
> +	if (pid)
> +		*pid = thread->pid_;
> +
> +	return thread->cpu;
> +}

What is the problem with:

	struct thread *thread = machine__find_thread(machine, tid);
	pid_t pid = thread->pid_;
	int cpu = thread->cpu;

In your case you'll have:

	int pid;
	int cpu = machine__get_thread_cpu(machine, tid, &pid);

Which is slightly more compact, but then we end up with a function that
from its name should just get a 'cpu' but also asks for the pid.

I think it is better to just use what we have (machine__find_thread),
have a 'thread' variable and then use any of its members, directly.

- ARnaldo
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