[PATCH v8 2/3]: perf record: enable asynchronous trace writing

[Alexey Budankov <alexey.budankov@linux.intel.com>]

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 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 | 128 +++++++++++++++++++++++++++++++++++++++++++-
 tools/perf/util/mmap.c      |  54 ++++++++++++++-----
 tools/perf/util/mmap.h      |   2 +-
 3 files changed, 169 insertions(+), 15 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 22ebeb92ac51..d4857572cf33 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -121,6 +121,93 @@ static int record__write(struct record *rec, void *bf, size_t size)
 	return 0;
 }
 
+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 process_synthesized_event(struct perf_tool *tool,
 				     union perf_event *event,
 				     struct perf_sample *sample __maybe_unused,
@@ -130,12 +217,27 @@ static int process_synthesized_event(struct perf_tool *tool,
 	return record__write(rec, event, event->header.size);
 }
 
-static int record__pushfn(void *to, void *bf, size_t size)
+static int record__pushfn(void *to, struct aiocb *cblock, void *data, size_t size)
 {
+	off_t off;
 	struct record *rec = to;
+	int ret, trace_fd = rec->session->data->file.fd;
 
 	rec->samples++;
-	return record__write(rec, bf, size);
+
+	off = lseek(trace_fd, 0, SEEK_CUR);
+	lseek(trace_fd, off + size, SEEK_SET);
+	ret = record__aio_write(cblock, trace_fd, data, 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;
 }
 
 static volatile int done;
@@ -510,6 +612,19 @@ static struct perf_event_header finished_round_event = {
 	.type = PERF_RECORD_FINISHED_ROUND,
 };
 
+static void record__mmap_read_sync(struct record *rec)
+{
+	int i;
+	struct perf_evlist *evlist = rec->evlist;
+	struct perf_mmap *maps = evlist->mmap;
+
+	for (i = 0; i < evlist->nr_mmaps; i++) {
+		struct perf_mmap *map = &maps[i];
+		if (map->base)
+			record__aio_sync(map);
+	}
+}
+
 static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evlist,
 				    bool overwrite)
 {
@@ -532,6 +647,11 @@ static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evli
 		struct auxtrace_mmap *mm = &maps[i].auxtrace_mmap;
 
 		if (maps[i].base) {
+			/*
+			 * Call record__aio_sync() to wait till map->data buffer
+			 * becomes available after previous aio write request.
+			 */
+			record__aio_sync(&maps[i]);
 			if (perf_mmap__push(&maps[i], rec, record__pushfn) != 0) {
 				rc = -1;
 				goto out;
@@ -1054,6 +1174,7 @@ 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;
@@ -1065,6 +1186,7 @@ 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;
@@ -1083,6 +1205,7 @@ 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);
 
 			/*
@@ -1136,6 +1259,7 @@ 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/util/mmap.c b/tools/perf/util/mmap.c
index e53038d76445..71c5628df3db 100644
--- a/tools/perf/util/mmap.c
+++ b/tools/perf/util/mmap.c
@@ -305,11 +305,11 @@ int perf_mmap__read_init(struct perf_mmap *map)
 }
 
 int perf_mmap__push(struct perf_mmap *md, void *to,
-		    int push(void *to, void *buf, size_t size))
+		    int push(void *to, struct aiocb *cblock, void *data, size_t size))
 {
 	u64 head = perf_mmap__read_head(md);
 	unsigned char *data = md->base + page_size;
-	unsigned long size;
+	unsigned long size, size0 = 0;
 	void *buf;
 	int rc = 0;
 
@@ -317,31 +317,61 @@ int perf_mmap__push(struct perf_mmap *md, void *to,
 	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;
-
-		if (push(to, buf, size) < 0) {
-			rc = -1;
-			goto out;
-		}
+		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);
 
-	if (push(to, buf, size) < 0) {
-		rc = -1;
-		goto out;
-	}
+	/*
+	 * 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);
-out:
+
+	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;
 }
 
diff --git a/tools/perf/util/mmap.h b/tools/perf/util/mmap.h
index 1974e621e36b..a9795a5fe200 100644
--- a/tools/perf/util/mmap.h
+++ b/tools/perf/util/mmap.h
@@ -95,7 +95,7 @@ union perf_event *perf_mmap__read_forward(struct perf_mmap *map);
 union perf_event *perf_mmap__read_event(struct perf_mmap *map);
 
 int perf_mmap__push(struct perf_mmap *md, void *to,
-		    int push(void *to, void *buf, size_t size));
+		    int push(void *to, struct aiocb *cblock, void *data, size_t size));
 
 size_t perf_mmap__mmap_len(struct perf_mmap *map);