linux-kernel - Re: [PATCH] perf probe: Add fastpath to do lookup by function name

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Date:	Thu, 24 Mar 2011 21:47:28 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf probe: Add fastpath to do lookup by function name

On Thu, 2011-03-24 at 17:08 +0800, Masami Hiramatsu wrote:
> (2011/03/25 0:38), Lin Ming wrote:
> > The vmlinux file may have thousands of CUs.
> > We can lookup function name from .debug_pubnames section
> > to avoid the slow loop on CUs.
> > 
> > Signed-off-by: Lin Ming <ming.m.lin@...el.com>
> > ---
> >  tools/perf/util/probe-finder.c |   38 ++++++++++++++++++++++++++++++++++++++
> >  tools/perf/util/probe-finder.h |    1 +
> >  2 files changed, 39 insertions(+), 0 deletions(-)
> > 
> > diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> > index 194f9e2..b2034c2 100644
> > --- a/tools/perf/util/probe-finder.c
> > +++ b/tools/perf/util/probe-finder.c
> > @@ -1876,6 +1876,30 @@ static int find_line_range_by_func(struct line_finder *lf)
> >  	return param.retval;
> >  }
> >  
> > +static int pubname_search_cb(Dwarf *dbg, Dwarf_Global *gl, void *data)
> > +{
> > +	struct line_finder *lf = data;
> > +	struct line_range *lr = lf->lr;
> > +
> > +	if (dwarf_offdie(dbg, gl->die_offset, &lf->sp_die)) {
> > +		if (dwarf_tag(&lf->sp_die) != DW_TAG_subprogram)
> > +			return DWARF_CB_OK;
> > +
> > +		if (die_compare_name(&lf->sp_die, lr->function)) {
> > +			if (!dwarf_offdie(dbg, gl->cu_offset, &lf->cu_die))
> > +				return DWARF_CB_OK;
> > +
> 
> Just one comment.
> Could you ensure that the decl_file of sp_die matches lr->file (by strtailcmp) here?

OK, so the file name compare with cu_find_realpath(..) can be removed,
as below.

This makes the lookup a bit more faster again.

Thanks, I'll post a new version with below changes.

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index b2034c2..38e4a05 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -1880,6 +1880,7 @@ static int pubname_search_cb(Dwarf *dbg, Dwarf_Global *gl, void *data)
 {
 	struct line_finder *lf = data;
 	struct line_range *lr = lf->lr;
+	const char *file;
 
 	if (dwarf_offdie(dbg, gl->die_offset, &lf->sp_die)) {
 		if (dwarf_tag(&lf->sp_die) != DW_TAG_subprogram)
@@ -1889,8 +1890,12 @@ static int pubname_search_cb(Dwarf *dbg, Dwarf_Global *gl, void *data)
 			if (!dwarf_offdie(dbg, gl->cu_offset, &lf->cu_die))
 				return DWARF_CB_OK;
 
-			if (lr->file && !cu_find_realpath(&lf->cu_die, lr->file))
-				return DWARF_CB_OK;
+			if (lr->file) {
+				file = dwarf_decl_file(&lf->sp_die);
+
+				if (file && strtailcmp(file, lr->file))
+					return DWARF_CB_OK;
+			}
 
 			lf->found = 1;
 			return DWARF_CB_ABORT;




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