linux-kernel - Re: [PATCH v3 1/2] perf tool: improves DSO long names search speed with RB tree

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Date:	Wed, 24 Sep 2014 11:29:07 -0400
From:	Waiman Long <waiman.long@...com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>,
	Don Zickus <dzickus@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH v3 1/2] perf tool: improves DSO long names search speed
 with RB tree

On 09/18/2014 11:10 AM, Arnaldo Carvalho de Melo wrote:
> Em Thu, Sep 18, 2014 at 09:30:20AM -0400, Waiman Long escreveu:
>> +++ b/tools/perf/util/dso.c
>> @@ -651,6 +651,80 @@ struct dso *dso__kernel_findnew(struct machine *machine, const char *name,
>>   	return dso;
>
>> +/*
>> + * RB root of DSOs sorted by the long name
>> + */
>> +struct rb_root dso__root = { NULL };
> Why do we still have a global variable for this? I thought that we would
> be having this in struct machine?
>
> Ok, I shouldn't have done this, but I went on and looked at the second
> patch, and there, this goes away, why not avoid introducing the global
> in the first place?

The global variable was added to make the first patch compilable by 
itself. I will take this out in the next version of the patch.

> I.e. the existing code operates on a data structure that holds struct
> dsos, you are switching to a new data structure, so it looked natural to
> me to do this in one step, no?

Yes, I think that makes sense.

> Also at some point I thought about adding rb_tree helper functions to do
> some rb__for_each() like operation, i.e. to sequentially access the
> rb_tree instead of using it for searching using its key. PeterZ
> rightfully nacked that because that would, IIRC, encourage people to use
> a rb_tree to do linear searches for normal operation, i.e. not just for
> rb_tree__printf() dump like routines:
>
> https://lkml.org/lkml/2010/1/13/227
>
> Also I saw at least one place where some foo__for_each_entry_safe() is
> used but the loop doesn't look like it will remove/add anything to the
> data structure that is being made "_safe", i.e. it should remain
> foo__for_each_entry(), as it was before.
>
> So, I would _keep_ the list_head, or else replace it with a another
> rb_node to do lookups on it by shortname the same way we do for long
> names.
>
> The cheapest thing now would be for solving your problem, i.e. use a
> rb_tree for searching for long names, keep the list_head for short names
> linear searches.
>
> I suggest having a
>
> struct dsos {
> 	struct list_head short_names;
> 	struct rb_root	 long_names;
> };
>
> Then make struct machine use this type for:
>
> 	struct dsos	kernel_dsos, user_dsos;
>
> Then all those dsos__find* routines stop receiving a list_head pointer
> and start receiving a "struct dsos" instance.
>
> That way it can add the dso to both containers, the one "sorted" by
> short names (that linear search, just like before) and to the rb_tree
> sorted by long names.
>
> - Arnaldo

I think this is a good idea. I will incorporate that in my next patch. 
BTW, the list isn't sorted in any way. So I won't use the same structure 
field names as you have suggested.


-Longman
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