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Subject[PATCH 41/44] perf evlist: Introduce side band thread
Date
From: Song Liu <songliubraving@fb.com>

This patch introduces side band thread that captures extended
information for events like PERF_RECORD_BPF_EVENT.

This new thread uses its own evlist that uses ring buffer with very low
watermark for lower latency.

To use side band thread, we need to:

1. add side band event(s) by calling perf_evlist__add_sb_event();
2. calls perf_evlist__start_sb_thread();
3. at the end of perf run, perf_evlist__stop_sb_thread().

In the next patch, we use this thread to handle PERF_RECORD_BPF_EVENT.

Committer notes:

Add fix by Jiri Olsa for when te sb_tread can't get started and then at
the end the stop_sb_thread() segfaults when joining the (non-existing)
thread.

That can happen when running 'perf top' or 'perf record' as a normal
user, for instance.

Further checks need to be done on top of this to more graciously handle
these possible failure scenarios.

Signed-off-by: Song Liu <songliubraving@fb.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stanislav Fomichev <sdf@google.com>
Link: http://lkml.kernel.org/r/20190312053051.2690567-15-songliubraving@fb.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/builtin-record.c | 9 +++
tools/perf/builtin-top.c | 9 +++
tools/perf/util/evlist.c | 119 ++++++++++++++++++++++++++++++++++++
tools/perf/util/evlist.h | 12 ++++
tools/perf/util/evsel.h | 6 ++
5 files changed, 155 insertions(+)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index e79faccd7842..6f645fd72fed 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1137,6 +1137,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
struct perf_data *data = &rec->data;
struct perf_session *session;
bool disabled = false, draining = false;
+ struct perf_evlist *sb_evlist = NULL;
int fd;

atexit(record__sig_exit);
@@ -1237,6 +1238,11 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
goto out_child;
}

+ if (perf_evlist__start_sb_thread(sb_evlist, &rec->opts.target)) {
+ pr_debug("Couldn't start the BPF side band thread:\nBPF programs starting from now on won't be annotatable\n");
+ opts->no_bpf_event = true;
+ }
+
err = record__synthesize(rec, false);
if (err < 0)
goto out_child;
@@ -1487,6 +1493,9 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)

out_delete_session:
perf_session__delete(session);
+
+ if (!opts->no_bpf_event)
+ perf_evlist__stop_sb_thread(sb_evlist);
return status;
}

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index c2ea22c4ea67..3ce8a8db6c1d 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -1501,6 +1501,7 @@ int cmd_top(int argc, const char **argv)
"number of thread to run event synthesize"),
OPT_END()
};
+ struct perf_evlist *sb_evlist = NULL;
const char * const top_usage[] = {
"perf top [<options>]",
NULL
@@ -1636,8 +1637,16 @@ int cmd_top(int argc, const char **argv)
goto out_delete_evlist;
}

+ if (perf_evlist__start_sb_thread(sb_evlist, target)) {
+ pr_debug("Couldn't start the BPF side band thread:\nBPF programs starting from now on won't be annotatable\n");
+ opts->no_bpf_event = true;
+ }
+
status = __cmd_top(&top);

+ if (!opts->no_bpf_event)
+ perf_evlist__stop_sb_thread(sb_evlist);
+
out_delete_evlist:
perf_evlist__delete(top.evlist);
perf_session__delete(top.session);
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index ed20f4379956..ec78e93085de 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -19,6 +19,7 @@
#include "debug.h"
#include "units.h"
#include "asm/bug.h"
+#include "bpf-event.h"
#include <signal.h>
#include <unistd.h>

@@ -1856,3 +1857,121 @@ struct perf_evsel *perf_evlist__reset_weak_group(struct perf_evlist *evsel_list,
}
return leader;
}
+
+int perf_evlist__add_sb_event(struct perf_evlist **evlist,
+ struct perf_event_attr *attr,
+ perf_evsel__sb_cb_t cb,
+ void *data)
+{
+ struct perf_evsel *evsel;
+ bool new_evlist = (*evlist) == NULL;
+
+ if (*evlist == NULL)
+ *evlist = perf_evlist__new();
+ if (*evlist == NULL)
+ return -1;
+
+ if (!attr->sample_id_all) {
+ pr_warning("enabling sample_id_all for all side band events\n");
+ attr->sample_id_all = 1;
+ }
+
+ evsel = perf_evsel__new_idx(attr, (*evlist)->nr_entries);
+ if (!evsel)
+ goto out_err;
+
+ evsel->side_band.cb = cb;
+ evsel->side_band.data = data;
+ perf_evlist__add(*evlist, evsel);
+ return 0;
+
+out_err:
+ if (new_evlist) {
+ perf_evlist__delete(*evlist);
+ *evlist = NULL;
+ }
+ return -1;
+}
+
+static void *perf_evlist__poll_thread(void *arg)
+{
+ struct perf_evlist *evlist = arg;
+ bool draining = false;
+ int i;
+
+ while (draining || !(evlist->thread.done)) {
+ if (draining)
+ draining = false;
+ else if (evlist->thread.done)
+ draining = true;
+
+ if (!draining)
+ perf_evlist__poll(evlist, 1000);
+
+ for (i = 0; i < evlist->nr_mmaps; i++) {
+ struct perf_mmap *map = &evlist->mmap[i];
+ union perf_event *event;
+
+ if (perf_mmap__read_init(map))
+ continue;
+ while ((event = perf_mmap__read_event(map)) != NULL) {
+ struct perf_evsel *evsel = perf_evlist__event2evsel(evlist, event);
+
+ if (evsel && evsel->side_band.cb)
+ evsel->side_band.cb(event, evsel->side_band.data);
+ else
+ pr_warning("cannot locate proper evsel for the side band event\n");
+
+ perf_mmap__consume(map);
+ }
+ perf_mmap__read_done(map);
+ }
+ }
+ return NULL;
+}
+
+int perf_evlist__start_sb_thread(struct perf_evlist *evlist,
+ struct target *target)
+{
+ struct perf_evsel *counter;
+
+ if (!evlist)
+ return 0;
+
+ if (perf_evlist__create_maps(evlist, target))
+ goto out_delete_evlist;
+
+ evlist__for_each_entry(evlist, counter) {
+ if (perf_evsel__open(counter, evlist->cpus,
+ evlist->threads) < 0)
+ goto out_delete_evlist;
+ }
+
+ if (perf_evlist__mmap(evlist, UINT_MAX))
+ goto out_delete_evlist;
+
+ evlist__for_each_entry(evlist, counter) {
+ if (perf_evsel__enable(counter))
+ goto out_delete_evlist;
+ }
+
+ evlist->thread.done = 0;
+ if (pthread_create(&evlist->thread.th, NULL, perf_evlist__poll_thread, evlist))
+ goto out_delete_evlist;
+
+ return 0;
+
+out_delete_evlist:
+ perf_evlist__delete(evlist);
+ evlist = NULL;
+ return -1;
+}
+
+void perf_evlist__stop_sb_thread(struct perf_evlist *evlist)
+{
+ if (!evlist)
+ return;
+ evlist->thread.done = 1;
+ pthread_join(evlist->thread.th, NULL);
+ perf_evlist__delete(evlist);
+}
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index 744906dd4887..dcb68f34d2cd 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -54,6 +54,10 @@ struct perf_evlist {
struct perf_sample *sample);
u64 first_sample_time;
u64 last_sample_time;
+ struct {
+ pthread_t th;
+ volatile int done;
+ } thread;
};

struct perf_evsel_str_handler {
@@ -87,6 +91,14 @@ int __perf_evlist__add_default_attrs(struct perf_evlist *evlist,

int perf_evlist__add_dummy(struct perf_evlist *evlist);

+int perf_evlist__add_sb_event(struct perf_evlist **evlist,
+ struct perf_event_attr *attr,
+ perf_evsel__sb_cb_t cb,
+ void *data);
+int perf_evlist__start_sb_thread(struct perf_evlist *evlist,
+ struct target *target);
+void perf_evlist__stop_sb_thread(struct perf_evlist *evlist);
+
int perf_evlist__add_newtp(struct perf_evlist *evlist,
const char *sys, const char *name, void *handler);

diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index cc578e02e08f..0f2c6c93d721 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -73,6 +73,8 @@ struct perf_evsel_config_term {

struct perf_stat_evsel;

+typedef int (perf_evsel__sb_cb_t)(union perf_event *event, void *data);
+
/** struct perf_evsel - event selector
*
* @evlist - evlist this evsel is in, if it is in one.
@@ -151,6 +153,10 @@ struct perf_evsel {
bool collect_stat;
bool weak_group;
const char *pmu_name;
+ struct {
+ perf_evsel__sb_cb_t *cb;
+ void *data;
+ } side_band;
};

union u64_swap {
--
2.20.1
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