linux-kernel - Re: [RFC/PATCH 17/38] perf tools: Maintain map groups list in a leader thread

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Date:	Thu, 8 Oct 2015 14:58:00 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Stephane Eranian <eranian@...gle.com>,
	David Ahern <dsahern@...il.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC/PATCH 17/38] perf tools: Maintain map groups list in a
 leader thread

On Fri, Oct 02, 2015 at 02:18:58PM +0900, Namhyung Kim wrote:

SNIP

>  int __thread__set_comm(struct thread *thread, const char *str, u64 timestamp,
>  		       bool exec)
>  {
> @@ -182,6 +257,40 @@ int __thread__set_comm(struct thread *thread, const char *str, u64 timestamp,
>  			unwind__flush_access(thread);
>  	}
>  
> +	if (exec) {
> +		struct machine *machine;
> +
> +		BUG_ON(thread->mg == NULL || thread->mg->machine == NULL);
> +
> +		machine = thread->mg->machine;
> +
> +		if (thread->tid != thread->pid_) {
> +			struct map_groups *old = thread->mg;
> +			struct thread *leader;
> +
> +			leader = machine__findnew_thread(machine, thread->pid_,
> +							 thread->pid_);
> +
> +			/* now it'll be a new leader */
> +			thread->pid_ = thread->tid;
> +
> +			thread->mg = map_groups__new(old->machine);
> +			if (thread->mg == NULL)
> +				return -ENOMEM;
> +
> +			/* save current mg in the new leader */
> +			thread__clone_map_groups(thread, leader);
> +
> +			/* current mg of leader thread needs one more refcnt */
> +			map_groups__get(thread->mg);
> +
> +			thread__set_map_groups(thread, thread->mg, old->timestamp);
> +		}
> +
> +		/* create a new mg for newly executed binary */
> +		thread__set_map_groups(thread, map_groups__new(machine), timestamp);

should this     ^^^^ be in the else case of above condition?

also thread__fork calls thread__clone_map_groups once again,
I have some difficulty to sort this out ATM.. is that correct?

some comment on how we treat map groups in general (for fork/clone/exit)
would be awesome ;-)

thanks,
jirka
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