linux-kernel - Re: [PATCH v4 2/2] perf tool: improves DSO long names lookup speed with rbtree

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Message-ID: <87d2afhy54.fsf@sejong.aot.lge.com>
Date:	Mon, 29 Sep 2014 13:02:47 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Waiman Long <Waiman.Long@...com>,
	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 v4 2/2] perf tool: improves DSO long names lookup speed with rbtree

On Fri, 26 Sep 2014 11:22:34 -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, Sep 24, 2014 at 11:45:40AM -0400, Waiman Long escreveu:
>> +	/*
>> +	 * Find node with the matching name
>> +	 */
>> +	while (*p) {
>> +		struct dso *this = rb_entry(*p, struct dso, rb_node);
>> +		long rc = (long)strcmp(name, this->long_name);
>> +
>> +		parent = *p;
>> +		if (rc == 0) {
>> +			/*
>> +			 * In case the new DSO is a duplicate of an existing
>> +			 * one, print an one-time warning & sort the entry
>> +			 * by its DSO address.
>> +			 */
>> +			if (!dso || (dso == this))
>> +				return this;	/* Find matching dso */
>> +			/*
>> +			 * The kernel DSOs may have duplicated long name,
>> +			 * so don't print warning for them.
>> +			 */
>> +			if (!warned && !strstr(name, "kernel.kallsyms")
>> +				    && !strstr(name, "/vmlinux")) {
>> +				pr_warning("Duplicated dso long name: %s\n",
>> +					   name);
>
> Huh? Can you elaborate on this? Ho can we add multiple DSOs with the
> exact same name into this tree? Have you actually seen this in practice?
> I guess so, judging by the comment above ("may have").

I guess it's because we split maps and dsos by section name (for kernel
only).  Please look at dso__load_sym() - If map_groups__find_by_name()
with short name + section name fails, it creates a new dso and map, and
then curr_dso->long_name will be set as dso->long_name.

Thanks,
Namhyung


>
> I'll try the patch to see if I get these warnings...
>
> But initial reaction to these long casts and fallbacking to pointer
> arithmetic for tree searching/inserting looked ugly :-\
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