Hi,

On 27.08.2018 0:48, Jiri Olsa wrote:

On Tue, Aug 21, 2018 at 11:27:03AM +0300, Alexey Budankov wrote:

SNIP

quoted

-static int record__pushfn(void *to, void *bf, size_t size)
+static int record__pushfn(void *to, void *bf, size_t size, off_t off)
 {
 	struct record *rec = to;
+	struct perf_mmap *map = bf;
 
 	rec->samples++;
-	return record__write(rec, bf, size);
+	return record__aio_write(rec->session->data->file.fd, &map->cblock,
+			map->data, size, off);
 }
 
 static volatile int done;

@@ -528,13 +530,85 @@ static struct perf_event_header finished_round_event = {
 	.type = PERF_RECORD_FINISHED_ROUND,
 };
 
+static int record__mmap_read_sync(int trace_fd, struct aiocb **cblocks,
+		int cblocks_size, struct record *rec)
+{
+	size_t rem;
+	ssize_t size;
+	off_t rem_off;
+	int i, aio_ret, aio_errno, do_suspend;
+	struct perf_mmap *md;
+	struct timespec timeout0 = { 0, 0 };
+	struct timespec timeoutS = { 0, 1000 * 500  * 1 };
+
+	if (!cblocks_size)
+		return 0;
+
+	do {
+		do_suspend = 0;
+		nanosleep(&timeoutS, NULL);

why the extra sleep in here and not sleeping through aio_suspend call?

Yep. Good question. That requires explicit explanation:

+               /* aio_suspend() implementation inside glibc (as of v2.27) is
+                * intrusive and not just blocks waiting io requests completion
+                * but polls requests queue inducing context switches in perf
+                * tool process. When profiling in system wide mode with tracing
+                * context switches the trace may be polluted by context switches
+                * from the perf process and the trace size becomes about 3-5
+                * times bigger than that of when writing the trace serially.
+                * To limit the volume of context switches from perf tool
+                * process nonsleep() call limits aio_suspend()
+                * polling till every half of the kernel timer tick which is
+                * usually 1ms (depends on CONFIG_HZ value).
+                */

jirka

quoted

+		if (aio_suspend((const struct aiocb**)cblocks, cblocks_size, &timeout0)) {
+			if (errno == EAGAIN || errno == EINTR) {
+				do_suspend = 1;
+				continue;
+			} else {
+				pr_err("failed to sync perf data, error: %m\n");

SNIP