Re: [PATCH] perf/powerpc: Cache the DWARF debug info

From: Sukadev Bhattiprolu
Date: Tue Oct 21 2014 - 20:11:00 EST


Arnaldo Carvalho de Melo [acme@xxxxxxxxxx] wrote:
| Em Tue, Oct 21, 2014 at 11:56:10AM -0700, Sukadev Bhattiprolu escreveu:
| > >From 773a3608a0cd2daf02e244cb9ffbf5bb6a0e724e Mon Sep 17 00:00:00 2001
| > From: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
| > Date: Tue, 21 Oct 2014 13:20:22 -0500
| > Subject: [PATCH 1/1] perf/powerpc: Cache DWARF debug info
|
| Jiri, isn't his related to that dsos caching thing you created?
|
| Anyway, there is a per machine struct (struct machine) where things like
| this should be put, please do not add globals or static variables in
| functions.

Good point. How about something like this:
---

Cache the DWARF debug info for DSO so we don't have to rebuild it for
each address in the DSO.

Note that dso__new() uses calloc() so don't need to set dso->dwfl
to NULL.

$ /tmp/perf.orig --version
perf version 3.18.rc1.gc2661b8
$ /tmp/perf.new --version
perf version 3.18.rc1.g402d62
$ perf stat -e cycles,instructions /tmp/perf.orig report -g > orig

Performance counter stats for '/tmp/perf.orig report -g':

6,428,177,183 cycles # 0.000 GHz
4,176,288,391 instructions # 0.65 insns per cycle

1.840666132 seconds time elapsed

$ perf stat -e cycles,instructions /tmp/perf.new report -g > new

Performance counter stats for '/tmp/perf.new report -g':

305,773,142 cycles # 0.000 GHz
276,048,272 instructions # 0.90 insns per cycle

0.087693543 seconds time elapsed
$ diff orig new
$

Changelog[v2]:
[Arnaldo Carvalho] Cache in existing global objects rather than create
new static/globals in functions.

Reported-by: Anton Blanchard <anton@xxxxxxxxx>
Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
---
tools/perf/arch/powerpc/util/skip-callchain-idx.c | 33 +++++++++++++++--------
tools/perf/util/dso.h | 1 +
2 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/tools/perf/arch/powerpc/util/skip-callchain-idx.c b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
index d73ef8b..9892b0f 100644
--- a/tools/perf/arch/powerpc/util/skip-callchain-idx.c
+++ b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
@@ -145,7 +145,7 @@ static Dwarf_Frame *get_dwarf_frame(Dwfl_Module *mod, Dwarf_Addr pc)
* yet used)
* -1 in case of errors
*/
-static int check_return_addr(const char *exec_file, Dwarf_Addr pc)
+static int check_return_addr(struct dso *dso, Dwarf_Addr pc)
{
int rc = -1;
Dwfl *dwfl;
@@ -156,15 +156,27 @@ static int check_return_addr(const char *exec_file, Dwarf_Addr pc)
Dwarf_Addr end = pc;
bool signalp;

- dwfl = dwfl_begin(&offline_callbacks);
- if (!dwfl) {
- pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));
- return -1;
- }
+ dwfl = dso->dwfl;

- if (dwfl_report_offline(dwfl, "", exec_file, -1) == NULL) {
- pr_debug("dwfl_report_offline() failed %s\n", dwarf_errmsg(-1));
- goto out;
+ if (!dwfl) {
+ dwfl = dwfl_begin(&offline_callbacks);
+ if (!dwfl) {
+ pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));
+ return -1;
+ }
+
+ if (dwfl_report_offline(dwfl, "", dso->long_name, -1) == NULL) {
+ pr_debug("dwfl_report_offline() failed %s\n",
+ dwarf_errmsg(-1));
+ /*
+ * We normally cache the DWARF debug info and never
+ * call dwfl_end(). But to prevent fd leak, free in
+ * case of error.
+ */
+ dwfl_end(dwfl);
+ goto out;
+ }
+ dso->dwfl = dwfl;
}

mod = dwfl_addrmodule(dwfl, pc);
@@ -194,7 +206,6 @@ static int check_return_addr(const char *exec_file, Dwarf_Addr pc)
rc = check_return_reg(ra_regno, frame);

out:
- dwfl_end(dwfl);
return rc;
}

@@ -246,7 +257,7 @@ int arch_skip_callchain_idx(struct machine *machine, struct thread *thread,
return skip_slot;
}

- rc = check_return_addr(dso->long_name, ip);
+ rc = check_return_addr(dso, ip);

pr_debug("DSO %s, nr %" PRIx64 ", ip 0x%" PRIx64 "rc %d\n",
dso->long_name, chain->nr, ip, rc);
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index acb651a..3c9b391 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -127,6 +127,7 @@ struct dso {
const char *long_name;
u16 long_name_len;
u16 short_name_len;
+ void *dwfl; /* DWARF debug info */

/* dso data file */
struct {

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