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Subject[PATCH v9 2/3]: perf record: enable asynchronous trace writing
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Date

Trace file offset is calculated and updated linearly prior
enqueuing aio write at record__pushfn().

record__aio_sync() blocks till completion of started AIO operation
and then proceeds.

record__mmap_read_sync() implements a barrier for all incomplete
aio write requests.

Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
---
Changes in v9:
- enable AIO streaming only when --aio-cblocks option is specified explicitly
Changes in v8:
- split AIO completion check into separate record__aio_complete()
Changes in v6:
- handled errno == EAGAIN case from aio_write();
Changes in v5:
- data loss metrics decreased from 25% to 2x in trialed configuration;
- avoided nanosleep() prior calling aio_suspend();
- switched to per cpu multi record__aio_sync() aio
- record_mmap_read_sync() now does global barrier just before
switching trace file or collection stop;
- resolved livelock on perf record -e intel_pt// -- dd if=/dev/zero of=/dev/null count=100000
Changes in v4:
- converted void *bf to struct perf_mmap *md in signatures
- written comment in perf_mmap__push() just before perf_mmap__get();
- written comment in record__mmap_read_sync() on possible restarting
of aio_write() operation and releasing perf_mmap object after all;
- added perf_mmap__put() for the cases of failed aio_write();
Changes in v3:
- written comments about nanosleep(0.5ms) call prior aio_suspend()
to cope with intrusiveness of its implementation in glibc;
- written comments about rationale behind coping profiling data
into mmap->data buffer;
---
tools/perf/builtin-record.c | 154 +++++++++++++++++++++++++++++++++++++++++++-
tools/perf/perf.h | 3 +
tools/perf/util/mmap.c | 73 +++++++++++++++++++++
tools/perf/util/mmap.h | 4 ++
4 files changed, 233 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 0980dfe3396b..c63fe8c021a2 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -124,6 +124,118 @@ static int record__write(struct record *rec, struct perf_mmap *map __maybe_unuse
return 0;
}

+#ifdef HAVE_AIO_SUPPORT
+static int record__aio_write(struct aiocb *cblock, int trace_fd,
+ void *buf, size_t size, off_t off)
+{
+ int rc;
+
+ cblock->aio_fildes = trace_fd;
+ cblock->aio_buf = buf;
+ cblock->aio_nbytes = size;
+ cblock->aio_offset = off;
+ cblock->aio_sigevent.sigev_notify = SIGEV_NONE;
+
+ do {
+ rc = aio_write(cblock);
+ if (rc == 0) {
+ break;
+ } else if (errno != EAGAIN) {
+ cblock->aio_fildes = -1;
+ pr_err("failed to queue perf data, error: %m\n");
+ break;
+ }
+ } while (1);
+
+ return rc;
+}
+
+static int record__aio_complete(struct perf_mmap *md, struct aiocb *cblock)
+{
+ void *rem_buf;
+ off_t rem_off;
+ size_t rem_size;
+ int rc, aio_errno;
+ ssize_t aio_ret, written;
+
+ aio_errno = aio_error(cblock);
+ if (aio_errno == EINPROGRESS)
+ return 0;
+
+ written = aio_ret = aio_return(cblock);
+ if (aio_ret < 0) {
+ if (aio_errno != EINTR)
+ pr_err("failed to write perf data, error: %m\n");
+ written = 0;
+ }
+
+ rem_size = cblock->aio_nbytes - written;
+
+ if (rem_size == 0) {
+ cblock->aio_fildes = -1;
+ /*
+ * md->refcount is incremented in perf_mmap__push() for
+ * every enqueued aio write request so decrement it because
+ * the request is now complete.
+ */
+ perf_mmap__put(md);
+ rc = 1;
+ } else {
+ /*
+ * aio write request may require restart with the
+ * reminder if the kernel didn't write whole
+ * chunk at once.
+ */
+ rem_off = cblock->aio_offset + written;
+ rem_buf = (void *)(cblock->aio_buf + written);
+ record__aio_write(cblock, cblock->aio_fildes,
+ rem_buf, rem_size, rem_off);
+ rc = 0;
+ }
+
+ return rc;
+}
+
+static void record__aio_sync(struct perf_mmap *md)
+{
+ struct aiocb *cblock = &md->cblock;
+ struct timespec timeout = { 0, 1000 * 1000 * 1 }; // 1ms
+
+ do {
+ if (cblock->aio_fildes == -1 || record__aio_complete(md, cblock))
+ return;
+
+ while (aio_suspend((const struct aiocb**)&cblock, 1, &timeout)) {
+ if (!(errno == EAGAIN || errno == EINTR))
+ pr_err("failed to sync perf data, error: %m\n");
+ }
+ } while (1);
+}
+
+static int record__aio_pushfn(void *to, struct aiocb *cblock, void *bf, size_t size)
+{
+ off_t off;
+ struct record *rec = to;
+ int ret, trace_fd = rec->session->data->file.fd;
+
+ rec->samples++;
+
+ off = lseek(trace_fd, 0, SEEK_CUR);
+ lseek(trace_fd, off + size, SEEK_SET);
+ ret = record__aio_write(cblock, trace_fd, bf, size, off);
+ if (!ret) {
+ rec->bytes_written += size;
+
+ if (switch_output_size(rec))
+ trigger_hit(&switch_output_trigger);
+ } else {
+ lseek(trace_fd, off, SEEK_SET);
+ }
+
+ return ret;
+}
+#endif
+
static int process_synthesized_event(struct perf_tool *tool,
union perf_event *event,
struct perf_sample *sample __maybe_unused,
@@ -136,7 +248,6 @@ static int process_synthesized_event(struct perf_tool *tool,
static int record__pushfn(struct perf_mmap *map, void *to, void *bf, size_t size)
{
struct record *rec = to;
-
rec->samples++;
return record__write(rec, map, bf, size);
}
@@ -513,6 +624,24 @@ static struct perf_event_header finished_round_event = {
.type = PERF_RECORD_FINISHED_ROUND,
};

+static void record__mmap_read_sync(struct record *rec __maybe_unused)
+{
+#ifdef HAVE_AIO_SUPPORT
+ int i;
+ struct perf_evlist *evlist = rec->evlist;
+ struct perf_mmap *maps = evlist->mmap;
+
+ if (!rec->opts.nr_cblocks)
+ return;
+
+ for (i = 0; i < evlist->nr_mmaps; i++) {
+ struct perf_mmap *map = &maps[i];
+ if (map->base)
+ record__aio_sync(map);
+ }
+#endif
+}
+
static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evlist,
bool overwrite)
{
@@ -535,10 +664,29 @@ static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evli
struct perf_mmap *map = &maps[i];

if (map->base) {
+#ifndef HAVE_AIO_SUPPORT
if (perf_mmap__push(map, rec, record__pushfn) != 0) {
rc = -1;
goto out;
}
+#else
+ if (!rec->opts.nr_cblocks) {
+ if (perf_mmap__push(map, rec, record__pushfn) != 0) {
+ rc = -1;
+ goto out;
+ }
+ } else {
+ /*
+ * Call record__aio_sync() to wait till map->data buffer
+ * becomes available after previous aio write request.
+ */
+ record__aio_sync(map);
+ if (perf_mmap__aio_push(map, rec, record__aio_pushfn) != 0) {
+ rc = -1;
+ goto out;
+ }
+ }
+#endif
}

if (map->auxtrace_mmap.base && !rec->opts.auxtrace_snapshot_mode &&
@@ -1057,6 +1205,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
perf_evlist__toggle_bkw_mmap(rec->evlist, BKW_MMAP_DATA_PENDING);

if (record__mmap_read_all(rec) < 0) {
+ record__mmap_read_sync(rec);
trigger_error(&auxtrace_snapshot_trigger);
trigger_error(&switch_output_trigger);
err = -1;
@@ -1068,6 +1217,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
if (!trigger_is_error(&auxtrace_snapshot_trigger))
record__read_auxtrace_snapshot(rec);
if (trigger_is_error(&auxtrace_snapshot_trigger)) {
+ record__mmap_read_sync(rec);
pr_err("AUX area tracing snapshot failed\n");
err = -1;
goto out_child;
@@ -1086,6 +1236,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
*/
if (rec->evlist->bkw_mmap_state == BKW_MMAP_RUNNING)
continue;
+ record__mmap_read_sync(rec);
trigger_ready(&switch_output_trigger);

/*
@@ -1139,6 +1290,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
disabled = true;
}
}
+ record__mmap_read_sync(rec);
trigger_off(&auxtrace_snapshot_trigger);
trigger_off(&switch_output_trigger);

diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index 21bf7f5a3cf5..ef700d8bb610 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -82,6 +82,9 @@ struct record_opts {
bool use_clockid;
clockid_t clockid;
unsigned int proc_map_timeout;
+#ifdef HAVE_AIO_SUPPORT
+ int nr_cblocks;
+#endif
};

struct option;
diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
index 5b3727b0c7c0..0a13e217458d 100644
--- a/tools/perf/util/mmap.c
+++ b/tools/perf/util/mmap.c
@@ -352,6 +352,79 @@ int perf_mmap__push(struct perf_mmap *md, void *to,
return rc;
}

+#ifdef HAVE_AIO_SUPPORT
+int perf_mmap__aio_push(struct perf_mmap *md, void *to,
+ int push(void *to, struct aiocb *cblock, void *buf, size_t size))
+{
+ u64 head = perf_mmap__read_head(md);
+ unsigned char *data = md->base + page_size;
+ unsigned long size, size0 = 0;
+ void *buf;
+ int rc = 0;
+
+ rc = perf_mmap__read_init(md);
+ if (rc < 0)
+ return (rc == -EAGAIN) ? 0 : -1;
+
+ /*
+ * md->base data is copied into md->data buffer to
+ * release space in the kernel buffer as fast as possible,
+ * thru perf_mmap__consume() below.
+ *
+ * That lets the kernel to proceed with storing more
+ * profiling data into the kernel buffer earlier than other
+ * per-cpu kernel buffers are handled.
+ *
+ * Coping can be done in two steps in case the chunk of
+ * profiling data crosses the upper bound of the kernel buffer.
+ * In this case we first move part of data from md->start
+ * till the upper bound and then the reminder from the
+ * beginning of the kernel buffer till the end of
+ * the data chunk.
+ */
+
+ size = md->end - md->start;
+
+ if ((md->start & md->mask) + size != (md->end & md->mask)) {
+ buf = &data[md->start & md->mask];
+ size = md->mask + 1 - (md->start & md->mask);
+ md->start += size;
+ memcpy(md->data, buf, size);
+ size0 = size;
+ }
+
+ buf = &data[md->start & md->mask];
+ size = md->end - md->start;
+ md->start += size;
+ memcpy(md->data + size0, buf, size);
+
+ /*
+ * Increment md->refcount to guard md->data buffer
+ * from premature deallocation because md object can be
+ * released earlier than aio write request started
+ * on mmap->data is complete.
+ *
+ * perf_mmap__put() is done at record__aio_complete()
+ * after started request completion.
+ */
+ perf_mmap__get(md);
+
+ md->prev = head;
+ perf_mmap__consume(md);
+
+ rc = push(to, &md->cblock, md->data, size0 + size);
+ if (rc) {
+ /*
+ * Decrement md->refcount back if aio write
+ * operation failed to start.
+ */
+ perf_mmap__put(md);
+ }
+
+ return rc;
+}
+#endif
+
/*
* Mandatory for overwrite mode
* The direction of overwrite mode is backward.
diff --git a/tools/perf/util/mmap.h b/tools/perf/util/mmap.h
index 1b63b6cc7cf9..ac011777c38f 100644
--- a/tools/perf/util/mmap.h
+++ b/tools/perf/util/mmap.h
@@ -105,6 +105,10 @@ union perf_event *perf_mmap__read_event(struct perf_mmap *map);

int perf_mmap__push(struct perf_mmap *md, void *to,
int push(struct perf_mmap *map, void *to, void *buf, size_t size));
+#ifdef HAVE_AIO_SUPPORT
+int perf_mmap__aio_push(struct perf_mmap *md, void *to,
+ int push(void *to, struct aiocb *cblock, void *buf, size_t size));
+#endif

size_t perf_mmap__mmap_len(struct perf_mmap *map);
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