[PATCH RFC V7 6/7] perf,tools: per-event callgraph support

From: Kan Liang
Date: Wed Jul 29 2015 - 12:58:01 EST

From: Kan Liang <kan.liang@xxxxxxxxx>

When multiple events are sampled it may not be needed to collect
callgraphs for all of them. The sample sites are usually nearby, and
it's enough to collect the callgraphs on a reference event (such as
precise cycles or precise instructions).
This patchkit adds the ability to turn off callgraphs and time stamp
per event. This in term can reduce sampling overhead and the size of the
perf.data. Furthermore, it makes collecting back traces and timestamps
possible when PEBS threshold > 1, which significantly reducing the
sampling overhead especially for frequently occurring events
(https://lkml.org/lkml/2015/5/10/196). For example, A slower event with
a larger period collects back traces/timestamps. Other more events run
fast with multi-pebs. The time stamps from the slower events can be used
to order the faster events. Their backtraces can give the user enough
hint to find the right spot.

Here are some examples and test results.

1. Comparing the elapsed time and perf.data size from "kernbench -M -H".

The test command for FULL callgraph and time support.
"perf record -e
'{cpu/cpu-cycles,period=100000/,cpu/instructions,period=20000/p}'
--call-graph fp --time"

The test command for PARTIAL callgraph and time support.
"perf record -e
'{cpu/cpu-cycles,call-graph=fp,time,period=100000/,
cpu/instructions,call-graph=no,time=0,period=20000/p}'"

The elapsed time for FULL is 24.3 Sec, while for PARTIAL is 16.9 Sec.
The perf.data size for FULL is 22.1 Gb, while for PARTIAL is 12.4 Gb.

2. Comparing the perf.data size and callgraph results.

The test command for FULL callgraph and time support.
"perf record -e
'{cpu/cpu-cycles,period=100000/pp,cpu/instructions,period=20000/p}'
--call-graph fp -- ./tchain_edit"

The test command for PARTIAL callgraph and time support.
"perf record -e
'{cpu/cpu-cycles,call-graph=fp,time,period=100000/pp,
cpu/instructions,call-graph=no,time=0,period=20000/p}'
-- ./tchain_edit"

The perf.data size for FULL is 43.2 MB, while for PARTIAL is 21.1 MB.
The callgraph is roughly the same.

The callgraph from FULL
# Samples: 87K of event
'cpu/cpu-cycles,call-graph=fp,time,period=100000/pp'
# Event count (approx.): 8760000000
#
# Children Self Command Shared Object Symbol
# ........ ........ ........... ..................
..........................................
#
99.98% 0.00% tchain_edit libc-2.15.so [.]
__libc_start_main
|
---__libc_start_main

99.97% 0.00% tchain_edit tchain_edit [.] main
|
---main
__libc_start_main

99.97% 0.00% tchain_edit tchain_edit [.] f1
|
---f1
main
__libc_start_main

99.85% 87.01% tchain_edit tchain_edit [.] f3
|
---f3
|
|--99.74%-- f2
| f1
| main
| __libc_start_main
--0.26%-- [...]
99.71% 0.12% tchain_edit tchain_edit [.] f2
|
---f2
f1
main
__libc_start_main

The callgraph from PARTIAL
# Samples: 417K of event
'cpu/instructions,call-graph=no,time=0,period=20000/p'
# Event count (approx.): 8346980000
#
# Children Self Command Shared Object Symbol
# ........ ........ ........... ................
..........................................
#
98.82% 0.00% tchain_edit libc-2.15.so [.]
__libc_start_main
|
---__libc_start_main

98.82% 0.00% tchain_edit tchain_edit [.] main
|
---main
__libc_start_main

98.82% 0.00% tchain_edit tchain_edit [.] f1
|
---f1
main
__libc_start_main

98.82% 98.28% tchain_edit tchain_edit [.] f3
|
---f3
|
|--0.53%-- f2
| f1
| main
| __libc_start_main
|
|--0.01%-- f1
| main
| __libc_start_main
--99.46%-- [...]
97.63% 0.03% tchain_edit tchain_edit [.] f2
|
---f2
f1
main
__libc_start_main

7.13% 0.03% tchain_edit [kernel.vmlinux] [k] do_nmi
|
---do_nmi
end_repeat_nmi
f3
f2
f1
main
__libc_start_main

Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>
---
tools/perf/Documentation/perf-record.txt | 4 +++
tools/perf/util/evsel.c | 57 ++++++++++++++++++++++++++++++--
tools/perf/util/evsel.h | 4 +++
tools/perf/util/parse-events.c | 12 +++++++
tools/perf/util/parse-events.h | 2 ++
tools/perf/util/parse-events.l | 2 ++
tools/perf/util/pmu.c | 3 +-
7 files changed, 81 insertions(+), 3 deletions(-)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 0d852d1..e633711 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -52,6 +52,10 @@ OPTIONS
- 'time': Disable/enable time stamping. Acceptable values are 1 for
enabling time stamping. 0 for disabling time stamping.
The default is 1.
+ - 'call-graph': Disable/enable callgraph. Acceptable str are "fp" for
+ FP mode, "dwarf" for DWARF mode, "lbr" for LBR mode and
+ "no" for disable callgraph.
+ - 'stack-size': user stack size for dwarf mode
Note: If user explicitly sets options which conflict with the params,
the value set by the params will be overridden.

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index f572f46..0d11c5e 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -588,11 +588,18 @@ perf_evsel__config_callgraph(struct perf_evsel *evsel,
}
}

-static void apply_config_terms(struct perf_evsel *evsel)
+static void apply_config_terms(struct perf_evsel *evsel,
+ struct record_opts *opts)
{
struct perf_evsel_config_term *term;
struct list_head *config_terms = &evsel->config_terms;
struct perf_event_attr *attr = &evsel->attr;
+ struct callchain_param param;
+ u32 dump_size = 0;
+ char *callgraph_buf = NULL;
+
+ /* callgraph default */
+ param.record_mode = callchain_param.record_mode;

list_for_each_entry(term, config_terms, list) {
switch (term->type) {
@@ -605,10 +612,56 @@ static void apply_config_terms(struct perf_evsel *evsel)
else
perf_evsel__reset_sample_bit(evsel, TIME);
break;
+ case PERF_EVSEL__CONFIG_TERM_CALLGRAPH:
+ callgraph_buf = term->val.callgraph;
+ break;
+ case PERF_EVSEL__CONFIG_TERM_STACK_USER:
+ dump_size = term->val.stack_user;
+ break;
default:
break;
}
}
+
+ /* User explicitly set per-event callgraph, clear the old setting and reset. */
+ if ((callgraph_buf != NULL) || (dump_size > 0)) {
+
+ /* parse callgraph parameters */
+ if (callgraph_buf != NULL) {
+ if (!strcmp(callgraph_buf, "no")) {
+ param.enabled = false;
+ param.record_mode = CALLCHAIN_NONE;
+ } else {
+ param.enabled = true;
+ if (parse_callchain_record_opt(callgraph_buf, &param)) {
+ pr_err("per-event callgraph setting for %s failed. "
+ "Apply callgraph global setting for it\n",
+ evsel->name);
+ return;
+ }
+ }
+ }
+ if (dump_size > 0)
+ param.dump_size = dump_size;
+
+ /* If global callgraph set, clear it */
+ if (callchain_param.enabled) {
+ perf_evsel__reset_sample_bit(evsel, CALLCHAIN);
+ if (callchain_param.record_mode == CALLCHAIN_LBR) {
+ perf_evsel__reset_sample_bit(evsel, BRANCH_STACK);
+ attr->branch_sample_type &= ~(PERF_SAMPLE_BRANCH_USER |
+ PERF_SAMPLE_BRANCH_CALL_STACK);
+ }
+ if (callchain_param.record_mode == CALLCHAIN_DWARF) {
+ perf_evsel__reset_sample_bit(evsel, REGS_USER);
+ perf_evsel__reset_sample_bit(evsel, STACK_USER);
+ }
+ }
+
+ /* set perf-event callgraph */
+ if (param.enabled)
+ perf_evsel__config_callgraph(evsel, opts, &param);
+ }
}

/*
@@ -807,7 +860,7 @@ void perf_evsel__config(struct perf_evsel *evsel, struct record_opts *opts)
* Apply event specific term settings,
* it overloads any global configuration.
*/
- apply_config_terms(evsel);
+ apply_config_terms(evsel, opts);
}

static int perf_evsel__alloc_fd(struct perf_evsel *evsel, int ncpus, int nthreads)
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 6a12908..09a3022 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -40,6 +40,8 @@ struct cgroup_sel;
enum {
PERF_EVSEL__CONFIG_TERM_PERIOD,
PERF_EVSEL__CONFIG_TERM_TIME,
+ PERF_EVSEL__CONFIG_TERM_CALLGRAPH,
+ PERF_EVSEL__CONFIG_TERM_STACK_USER,
PERF_EVSEL__CONFIG_TERM_MAX,
};

@@ -49,6 +51,8 @@ struct perf_evsel_config_term {
union {
u64 period;
bool time;
+ char *callgraph;
+ u64 stack_user;
} val;
};

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index a6cb9af..716f1fc 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -611,6 +611,12 @@ do { \
return -EINVAL;
}
break;
+ case PARSE_EVENTS__TERM_TYPE_CALLGRAPH:
+ CHECK_TYPE_VAL(STR);
+ break;
+ case PARSE_EVENTS__TERM_TYPE_STACKSIZE:
+ CHECK_TYPE_VAL(NUM);
+ break;
case PARSE_EVENTS__TERM_TYPE_NAME:
CHECK_TYPE_VAL(STR);
break;
@@ -662,6 +668,12 @@ do { \
case PARSE_EVENTS__TERM_TYPE_TIME:
ADD_CONFIG_TERM(TIME, time, term->val.num);
break;
+ case PARSE_EVENTS__TERM_TYPE_CALLGRAPH:
+ ADD_CONFIG_TERM(CALLGRAPH, callgraph, term->val.str);
+ break;
+ case PARSE_EVENTS__TERM_TYPE_STACKSIZE:
+ ADD_CONFIG_TERM(STACK_USER, stack_user, term->val.num);
+ break;
default:
break;
}
diff --git a/tools/perf/util/parse-events.h b/tools/perf/util/parse-events.h
index e6f9aacc..87dc9f6 100644
--- a/tools/perf/util/parse-events.h
+++ b/tools/perf/util/parse-events.h
@@ -64,6 +64,8 @@ enum {
PARSE_EVENTS__TERM_TYPE_SAMPLE_PERIOD,
PARSE_EVENTS__TERM_TYPE_BRANCH_SAMPLE_TYPE,
PARSE_EVENTS__TERM_TYPE_TIME,
+ PARSE_EVENTS__TERM_TYPE_CALLGRAPH,
+ PARSE_EVENTS__TERM_TYPE_STACKSIZE,
};

struct parse_events_term {
diff --git a/tools/perf/util/parse-events.l b/tools/perf/util/parse-events.l
index f542750..1665497 100644
--- a/tools/perf/util/parse-events.l
+++ b/tools/perf/util/parse-events.l
@@ -184,6 +184,8 @@ name { return term(yyscanner, PARSE_EVENTS__TERM_TYPE_NAME); }
period { return term(yyscanner, PARSE_EVENTS__TERM_TYPE_SAMPLE_PERIOD); }
branch_type { return term(yyscanner, PARSE_EVENTS__TERM_TYPE_BRANCH_SAMPLE_TYPE); }
time { return term(yyscanner, PARSE_EVENTS__TERM_TYPE_TIME); }
+call-graph { return term(yyscanner, PARSE_EVENTS__TERM_TYPE_CALLGRAPH); }
+stack-size { return term(yyscanner, PARSE_EVENTS__TERM_TYPE_STACKSIZE); }
, { return ','; }
"/" { BEGIN(INITIAL); return '/'; }
{name_minus} { return str(yyscanner, PE_NAME); }
diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index b615cdf..948f896 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -607,7 +607,8 @@ static char *formats_error_string(struct list_head *formats)
{
struct perf_pmu_format *format;
char *err, *str;
- static const char *static_terms = "config,config1,config2,name,period,branch_type,time\n";
+ static const char *static_terms = "config,config1,config2,name,period,"
+ "branch_type,time,call-graph,stack-size\n";
unsigned i = 0;

if (!asprintf(&str, "valid terms:"))
--
1.8.3.1

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