[PATCH v7 2/2]: perf record: enable asynchronous trace writing

From: Alexey Budankov
Date: Wed Sep 05 2018 - 03:39:37 EST


record__aio_sync() allocates index of free map->data buffer for
a cpu buffer or blocks till completion of any started operation
and then proceeds.

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

record__mmap_read_sync() implements a barrier for all incomplete
aio write requests per-cpu per aio data.

Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
---
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 | 182 +++++++++++++++++++++++++++++++++++++++++++-
tools/perf/util/mmap.c | 57 ++++++++++----
tools/perf/util/mmap.h | 4 +-
3 files changed, 223 insertions(+), 20 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index f17a6f9cb1ba..dbafc60c6bd7 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -121,6 +121,91 @@ 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_sync(struct perf_mmap *md)
+{
+ void *rem_buf;
+ off_t rem_off;
+ size_t rem_size;
+ ssize_t aio_ret, written;
+ int i, aio_errno, do_suspend, idx = -1;
+ struct aiocb **cblocks = md->cblocks;
+ struct timespec timeout = { 0, 1000 * 1000 * 1 }; // 1ms
+
+ for (i = 0; i < md->nr_cblocks; ++i)
+ if (cblocks[i]->aio_fildes == -1)
+ return i;
+
+ do {
+ do_suspend = 0;
+ if (aio_suspend((const struct aiocb**)cblocks, md->nr_cblocks, &timeout)) {
+ if (!(errno == EAGAIN || errno == EINTR))
+ pr_err("failed to sync perf data, error: %m\n");
+ do_suspend = 1;
+ continue;
+ }
+ for (i = 0; i < md->nr_cblocks; ++i) {
+ aio_errno = aio_error(cblocks[i]);
+ if (aio_errno == EINPROGRESS)
+ continue;
+ written = aio_ret = aio_return(cblocks[i]);
+ if (aio_ret < 0) {
+ if (aio_errno != EINTR)
+ pr_err("failed to write perf data, error: %m\n");
+ written = 0;
+ }
+ rem_size = cblocks[i]->aio_nbytes - written;
+ if (rem_size == 0) {
+ cblocks[i]->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);
+ if (idx == -1)
+ idx = i;
+ } else {
+ /* aio write request may require restart with the
+ * reminder if the kernel didn't write whole
+ * chunk at once.
+ */
+ rem_off = cblocks[i]->aio_offset + written;
+ rem_buf = (void*)(cblocks[i]->aio_buf + written);
+ record__aio_write(cblocks[i], cblocks[i]->aio_fildes,
+ rem_buf, rem_size, rem_off);
+ }
+ }
+ if (idx == -1)
+ do_suspend = 1;
+ } while (do_suspend);
+
+ return idx;
+}
+
static int process_synthesized_event(struct perf_tool *tool,
union perf_event *event,
struct perf_sample *sample __maybe_unused,
@@ -130,12 +215,28 @@ 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;
@@ -511,6 +612,70 @@ static struct perf_event_header finished_round_event = {
.type = PERF_RECORD_FINISHED_ROUND,
};

+static void record__aio_complete(struct perf_mmap *md, int i)
+{
+ int aio_errno;
+ void *rem_buf;
+ off_t rem_off;
+ size_t rem_size;
+ ssize_t aio_ret, written;
+ struct aiocb *cblock = md->cblocks[i];
+ struct timespec timeout = { 0, 1000 * 1000 * 1 }; // 1ms
+
+ if (cblock->aio_fildes == -1)
+ return;
+
+ do {
+ if (aio_suspend((const struct aiocb**)&cblock, 1, &timeout)) {
+ if (!(errno == EAGAIN || errno == EINTR))
+ pr_err("failed to sync perf data, error: %m\n");
+ continue;
+ }
+ aio_errno = aio_error(cblock);
+ if (aio_errno == EINPROGRESS)
+ continue;
+ 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);
+ return;
+ } 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);
+ }
+ } while (1);
+}
+
+static void record__mmap_read_sync(struct record *rec)
+{
+ int i, j;
+ 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)
+ for (j = 0; j < map->nr_cblocks; ++j)
+ record__aio_complete(map, j);
+ }
+}
+
static int record__mmap_read_evlist(struct record *rec, struct perf_evlist *evlist,
bool overwrite)
{
@@ -533,7 +698,13 @@ 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) {
- if (perf_mmap__push(&maps[i], rec, record__pushfn) != 0) {
+ /* Call record__aio_sync() to allocate free
+ * map->data buffer or wait till one of the
+ * buffers becomes available after previous
+ * aio write request.
+ */
+ if (perf_mmap__push(&maps[i], rec, record__aio_sync(&maps[i]),
+ record__pushfn) != 0) {
rc = -1;
goto out;
}
@@ -1055,6 +1226,7 @@ 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;
@@ -1066,6 +1238,7 @@ 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;
@@ -1084,6 +1257,8 @@ 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);

/*
@@ -1137,6 +1312,7 @@ 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 384d17cd1379..1d57d8387caf 100644
--- a/tools/perf/util/mmap.c
+++ b/tools/perf/util/mmap.c
@@ -332,12 +332,12 @@ int perf_mmap__read_init(struct perf_mmap *map)
return __perf_mmap__read_init(map);
}

-int perf_mmap__push(struct perf_mmap *md, void *to,
- int push(void *to, void *buf, size_t size))
+int perf_mmap__push(struct perf_mmap *md, void *to, int idx,
+ 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;

@@ -345,31 +345,58 @@ 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[idx] 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;
- }
+ size0 = md->mask + 1 - (md->start & md->mask);
+ md->start += size0;
+ memcpy(md->data[idx], buf, size0);
}

buf = &data[md->start & md->mask];
size = md->end - md->start;
md->start += size;
+ memcpy(md->data[idx] + size0, buf, size);

- if (push(to, buf, size) < 0) {
- rc = -1;
- goto out;
- }
+ /* Increment md->refcount to guard md->data[idx] buffer
+ * from premature deallocation because md object can be
+ * released earlier than aio write request started
+ * on mmap->data[idx] is complete.
+ *
+ * perf_mmap__put() is done at record__aio_sync() or
+ * record__aio_complete() after started request completion.
+ */
+
+ perf_mmap__get(md);

md->prev = head;
perf_mmap__consume(md);
-out:
+
+ rc = push(to, md->cblocks[idx], md->data[idx], 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 4a9bb0ecae4f..9a106c075172 100644
--- a/tools/perf/util/mmap.h
+++ b/tools/perf/util/mmap.h
@@ -95,8 +95,8 @@ 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 perf_mmap__push(struct perf_mmap *md, void *to, int aio_idx,
+ int push(void *to, struct aiocb *cblock, void *data, size_t size));

size_t perf_mmap__mmap_len(struct perf_mmap *map);