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Subject[PATCH v2 -tip] perf probe: Add fastpath to do lookup by function name
From
Date
v2 -> v1:
- Don't compare file names with cu_find_realpath(...), instead, compare them
with the name returned by dwarf_decl_file(sp_die)

The vmlinux file may have thousands of CUs.
We can lookup function name from .debug_pubnames section
to avoid the slow loop on CUs.

./perf stat -r 10 -- ./perf probe -k /home/mlin/vmlinux \
-s /home/mlin/linux-2.6 \
--line csum_partial_copy_to_user > tmp.log

before patch applied
=====================
364.535892 task-clock-msecs # 0.997 CPUs
0 context-switches # 0.000 M/sec
0 CPU-migrations # 0.000 M/sec
29,993 page-faults # 0.082 M/sec
865,862,109 cycles # 2375.245 M/sec
1,255,259,630 instructions # 1.450 IPC
252,400,884 branches # 692.390 M/sec
3,429,376 branch-misses # 1.359 %
1,386,990 cache-references # 3.805 M/sec
687,188 cache-misses # 1.885 M/sec

0.365792170 seconds time elapsed

after patch applied
=====================
89.896405 task-clock-msecs # 0.991 CPUs
1 context-switches # 0.000 M/sec
0 CPU-migrations # 0.000 M/sec
10,145 page-faults # 0.113 M/sec
214,553,875 cycles # 2386.679 M/sec
226,915,559 instructions # 1.058 IPC
44,536,614 branches # 495.422 M/sec
613,074 branch-misses # 1.377 %
860,787 cache-references # 9.575 M/sec
442,380 cache-misses # 4.921 M/sec

0.090716032 seconds time elapsed

Signed-off-by: Lin Ming <ming.m.lin@intel.com>
---
tools/perf/util/probe-finder.c | 39 +++++++++++++++++++++++++++++++++++++++
tools/perf/util/probe-finder.h | 1 +
2 files changed, 40 insertions(+), 0 deletions(-)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 194f9e2..5cf044c 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -1876,6 +1876,31 @@ 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;
+
+ if (lr->file &&
+ strtailcmp(lr->file, dwarf_decl_file(&lf->sp_die)))
+ return DWARF_CB_OK;
+
+ lf->found = 1;
+ return DWARF_CB_ABORT;
+ }
+ }
+
+ return DWARF_CB_OK;
+}
+
int find_line_range(int fd, struct line_range *lr)
{
struct line_finder lf = {.lr = lr, .found = 0};
@@ -1895,6 +1920,19 @@ int find_line_range(int fd, struct line_range *lr)
return -EBADF;
}

+ /* Fastpath: lookup by function name from .debug_pubnames section */
+ if (lr->function) {
+ struct dwarf_callback_param param = {.data = (void *)&lf, .retval = 0};
+
+ dwarf_getpubnames(dbg, pubname_search_cb, &lf, 0);
+ if (lf.found) {
+ lf.found = 0;
+ line_range_search_cb(&lf.sp_die, &param);
+ if (lf.found)
+ goto found;
+ }
+ }
+
/* Loop on CUs (Compilation Unit) */
while (!lf.found && ret >= 0) {
if (dwarf_nextcu(dbg, off, &noff, &cuhl, NULL, NULL, NULL) != 0)
@@ -1923,6 +1961,7 @@ int find_line_range(int fd, struct line_range *lr)
off = noff;
}

+found:
/* Store comp_dir */
if (lf.found) {
comp_dir = cu_get_comp_dir(&lf.cu_die);
diff --git a/tools/perf/util/probe-finder.h b/tools/perf/util/probe-finder.h
index beaefc3..4bc56a4 100644
--- a/tools/perf/util/probe-finder.h
+++ b/tools/perf/util/probe-finder.h
@@ -83,6 +83,7 @@ struct line_finder {
int lno_s; /* Start line number */
int lno_e; /* End line number */
Dwarf_Die cu_die; /* Current CU */
+ Dwarf_Die sp_die;
int found;
};

--
1.7.2.3




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