linux-kernel - Re: [PATCH] perf: Don't clone maps from parent when synthesizing forks

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Date:   Wed, 31 Oct 2018 10:06:45 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: Don't clone maps from parent when synthesizing
 forks

Em Wed, Oct 31, 2018 at 02:01:38PM +0100, Jiri Olsa escreveu:
> On Tue, Oct 30, 2018 at 10:24:04PM -0700, David Miller wrote:
> 
> SNIP
> 
> > diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> > index 111ae858cbcb..214b7979c4e7 100644
> > --- a/tools/perf/util/machine.c
> > +++ b/tools/perf/util/machine.c
> > @@ -1708,6 +1708,7 @@ int machine__process_fork_event(struct machine *machine, union perf_event *event
> >  	struct thread *parent = machine__findnew_thread(machine,
> >  							event->fork.ppid,
> >  							event->fork.ptid);
> > +	bool do_maps_clone = true;
> >  	int err = 0;
> >  
> >  	if (dump_trace)
> > @@ -1737,8 +1738,11 @@ int machine__process_fork_event(struct machine *machine, union perf_event *event
> >  	thread = machine__findnew_thread(machine, event->fork.pid,
> >  					 event->fork.tid);
> >  
> > +	if (event->fork.header.misc & PERF_RECORD_MISC_FORK_EXEC)
> > +		do_maps_clone = false;
> 
> could you please put some comment in here shortly
> explaining the reason behind this flag

I'll get that comment from the commit log message
 
> > +
> >  	if (thread == NULL || parent == NULL ||
> > -	    thread__fork(thread, parent, sample->time) < 0) {
> > +	    thread__fork(thread, parent, sample->time, do_maps_clone) < 0) {
> >  		dump_printf("problem processing PERF_RECORD_FORK, skipping event.\n");
> >  		err = -1;
> >  	}
> > diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
> > index 2048d393ece6..54b2c9ceba9f 100644
> > --- a/tools/perf/util/thread.c
> > +++ b/tools/perf/util/thread.c
> > @@ -330,7 +330,8 @@ static int thread__prepare_access(struct thread *thread)
> >  }
> >  
> >  static int thread__clone_map_groups(struct thread *thread,
> > -				    struct thread *parent)
> > +				    struct thread *parent,
> > +				    bool do_maps_clone)
> >  {
> >  	/* This is new thread, we share map groups for process. */
> >  	if (thread->pid_ == parent->pid_)
> > @@ -341,15 +342,14 @@ static int thread__clone_map_groups(struct thread *thread,
> >  			 thread->pid_, thread->tid, parent->pid_, parent->tid);
> >  		return 0;
> >  	}
> > -
> >  	/* But this one is new process, copy maps. */
> > -	if (map_groups__clone(thread, parent->mg) < 0)
> > +	if (do_maps_clone &&
> > +	    map_groups__clone(thread, parent->mg) < 0)
> >  		return -ENOMEM;
> > -
> >  	return 0;
> 
> we could move all this into one line:
> 
> 	return do_maps_clone ? map_groups__clone(thread, parent->mg) : 0;

Yeah, I can do that as well, after looking at what map_groups__clone()
returns, which can go into the unwind backends.

- Arnaldo
 
> thanks,
> jirka
> 
> >  }
> >  
> > -int thread__fork(struct thread *thread, struct thread *parent, u64 timestamp)
> > +int thread__fork(struct thread *thread, struct thread *parent, u64 timestamp, bool do_maps_clone)
> >  {
> >  	if (parent->comm_set) {
> >  		const char *comm = thread__comm_str(parent);
> > @@ -362,7 +362,7 @@ int thread__fork(struct thread *thread, struct thread *parent, u64 timestamp)
> >  	}
> >  
> >  	thread->ppid = parent->tid;
> > -	return thread__clone_map_groups(thread, parent);
> > +	return thread__clone_map_groups(thread, parent, do_maps_clone);
> >  }
> >  
> >  void thread__find_cpumode_addr_location(struct thread *thread, u64 addr,
> > diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
> > index 07606aa6998d..7e30fe99b74b 100644
> > --- a/tools/perf/util/thread.h
> > +++ b/tools/perf/util/thread.h
> > @@ -87,7 +87,7 @@ struct comm *thread__comm(const struct thread *thread);
> >  struct comm *thread__exec_comm(const struct thread *thread);
> >  const char *thread__comm_str(const struct thread *thread);
> >  int thread__insert_map(struct thread *thread, struct map *map);
> > -int thread__fork(struct thread *thread, struct thread *parent, u64 timestamp);
> > +int thread__fork(struct thread *thread, struct thread *parent, u64 timestamp, bool do_maps_clone);
> >  size_t thread__fprintf(struct thread *thread, FILE *fp);
> >  
> >  struct thread *thread__main_thread(struct machine *machine, struct thread *thread);