[PATCH V3 09/13] perf report: Add option to enable the LBR stitching approach

From: kan . liang
Date: Tue Oct 22 2019 - 13:12:30 EST


From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

With the LBR stitching approach, the reconstructed LBR call stack
can break the HW limitation. However, it may reconstruct invalid call
stacks in some cases, e.g. exception handing such as setjmp/longjmp.
Also, it may impact the processing time especially when the number of
samples with stitched LBRs are huge.

Add an option to enable the approach.

# To display the perf.data header info, please use
# --header/--header-only options.
#
#
# Total Lost Samples: 0
#
# Samples: 6K of event 'cycles'
# Event count (approx.): 6492797701
#
# Children Self Command Shared Object Symbol
# ........ ........ ............... ..................
# .................................
#
99.99% 99.99% tchain_edit tchain_edit [.] f43
|
---main
f1
f2
f3
f4
f5
f6
f7
f8
f9
f10
f11
f12
f13
f14
f15
f16
f17
f18
f19
f20
f21
f22
f23
f24
f25
f26
f27
f28
f29
f30
f31
|
--99.65%--f32
f33
f34
f35
f36
f37
f38
f39
f40
f41
f42
f43

Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
---
tools/perf/Documentation/perf-report.txt | 11 +++++++++++
tools/perf/builtin-report.c | 6 ++++++
2 files changed, 17 insertions(+)

diff --git a/tools/perf/Documentation/perf-report.txt b/tools/perf/Documentation/perf-report.txt
index 7315f155803f..c0651b68ed5d 100644
--- a/tools/perf/Documentation/perf-report.txt
+++ b/tools/perf/Documentation/perf-report.txt
@@ -476,6 +476,17 @@ include::itrace.txt[]
This option extends the perf report to show reference callgraphs,
which collected by reference event, in no callgraph event.

+--stitch-lbr::
+ Show callgraph with stitched LBRs, which may have more complete
+ callgraph. The perf.data file must have been obtained using
+ perf record --call-graph lbr.
+ Disabled by default. In common cases with call stack overflows,
+ it can recreate better call stacks than the default lbr call stack
+ output. But this approach is not full proof. There can be cases
+ where it creates incorrect call stacks from incorrect matches.
+ The known limitations include exception handing such as
+ setjmp/longjmp will have calls/returns not match.
+
--socket-filter::
Only report the samples on the processor socket that match with this filter

diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 7accaf8ef689..783dd5ec0db5 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -83,6 +83,7 @@ struct report {
bool header_only;
bool nonany_branch_mode;
bool group_set;
+ bool stitch_lbr;
int max_stack;
struct perf_read_values show_threads_values;
struct annotation_options annotation_opts;
@@ -263,6 +264,9 @@ static int process_sample_event(struct perf_tool *tool,
return -1;
}

+ if (rep->stitch_lbr)
+ al.thread->lbr_stitch_enable = true;
+
if (symbol_conf.hide_unresolved && al.sym == NULL)
goto out_put;

@@ -1190,6 +1194,8 @@ int cmd_report(int argc, const char **argv)
"Show full source file name path for source lines"),
OPT_BOOLEAN(0, "show-ref-call-graph", &symbol_conf.show_ref_callgraph,
"Show callgraph from reference event"),
+ OPT_BOOLEAN(0, "stitch-lbr", &report.stitch_lbr,
+ "Enable LBR callgraph stitching approach"),
OPT_INTEGER(0, "socket-filter", &report.socket_filter,
"only show processor socket that match with this filter"),
OPT_BOOLEAN(0, "raw-trace", &symbol_conf.raw_trace,
--
2.17.1