linux-kernel - Re: [PATCH 14/37] perf tools: Convert dead thread list into rbtree

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Date:	Fri, 26 Dec 2014 11:26:16 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
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>,
	David Ahern <dsahern@...il.com>,
	Stephane Eranian <eranian@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 14/37] perf tools: Convert dead thread list into rbtree

On Fri, Dec 26, 2014 at 8:05 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> On Wed, Dec 24, 2014 at 04:15:10PM +0900, Namhyung Kim wrote:
>
> SNIP
>
>>
>>  static void machine__remove_thread(struct machine *machine, struct thread *th)
>>  {
>> +     struct rb_node **p = &machine->dead_threads.rb_node;
>> +     struct rb_node *parent = NULL;
>> +     struct thread *pos;
>> +
>>       machine->last_match = NULL;
>>       rb_erase(&th->rb_node, &machine->threads);
>> +
>> +     th->dead = true;
>> +
>>       /*
>>        * We may have references to this thread, for instance in some hist_entry
>> -      * instances, so just move them to a separate list.
>> +      * instances, so just move them to a separate list in rbtree.
>>        */
>> -     list_add_tail(&th->node, &machine->dead_threads);
>> +     while (*p != NULL) {
>> +             parent = *p;
>> +             pos = rb_entry(parent, struct thread, rb_node);
>> +
>> +             if (pos->tid == th->tid) {
>> +                     list_add_tail(&th->node, &pos->node);
>> +                     return;
>> +             }
>
> hum, why is this 'new list' in thread object necessary? why not
> to store all in the tree?

No absolute reason, but I just wanted to keep them in a single place
and to see how many of them exist easily.  We could compare pid and
then timestamp so that it can be in a single rbtree.

>
>
>> +
>> +             if (th->tid < pos->tid)
>> +                     p = &(*p)->rb_left;
>> +             else
>> +                     p = &(*p)->rb_right;
>> +     }
>> +
>
> SNIP
>
>> diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
>> index 0b6dcd70bc8b..413f28cf689b 100644
>> --- a/tools/perf/util/thread.h
>> +++ b/tools/perf/util/thread.h
>> @@ -11,10 +11,8 @@
>>  struct thread_stack;
>>
>>  struct thread {
>> -     union {
>> -             struct rb_node   rb_node;
>> -             struct list_head node;
>> -     };
>> +     struct rb_node          rb_node;
>> +     struct list_head        node;
>>       struct map_groups       *mg;
>>       pid_t                   pid_; /* Not all tools update this */
>>       pid_t                   tid;
>> @@ -22,7 +20,8 @@ struct thread {
>>       int                     cpu;
>>       char                    shortname[3];
>>       bool                    comm_set;
>> -     bool                    dead; /* if set thread has exited */
>> +     bool                    exited; /* if set thread has exited */
>> +     bool                    dead; /* thread is in dead_threads list */
>
> looks like this also changes the logic (new exited flag),
> not just the dead threads storage wheel

AFAICS the 'dead' flag is not used other than thread__exited().  And
it confused me a dead thread might not be in a dead_threads tree (or
list).  So I changed the name and no logical change intended.

Thanks,
Namhyung
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