hwtracing: hisi_ptt: Optimize the trace data committing

In the current implementation, there're 4*4MiB trace buffer and hardware
will fill the buffer one by one. The driver will get notified if one
buffer is full and then copy data to the AUX buffer. If there's no
enough room for the next trace buffer, we'll commit the AUX buffer to
the perf core and try to apply a new one. In a typical configuration
the AUX buffer will be 16MiB, so we'll commit the data after the whole
AUX buffer is occupied. Then the driver cannot apply a new AUX buffer
immediately until the committed data is consumed by userspace and then
there's room in the AUX buffer again.

This patch tries to optimize this by commit the data after one single
trace buffer is filled. Since there's still room in the AUX buffer,
driver can apply a new one without failure and don't need to wait for
the userspace to consume the data.
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20231010084731.30450-4-yangyicong@huawei.com

drivers/hwtracing/ptt/hisi_ptt.c

@@ -274,15 +274,14 @@ static int hisi_ptt_update_aux(struct hisi_ptt *hisi_ptt, int index, bool stop)
 	buf->pos += size;
 
 	/*
-	 * Just commit the traced data if we're going to stop. Otherwise if the
-	 * resident AUX buffer cannot contain the data of next trace buffer,
-	 * apply a new one.
+	 * Always commit the data to the AUX buffer in time to make sure
+	 * userspace got enough time to consume the data.
+	 *
+	 * If we're not going to stop, apply a new one and check whether
+	 * there's enough room for the next trace.
 	 */
-	if (stop) {
-		perf_aux_output_end(handle, buf->pos);
-	} else if (buf->length - buf->pos < HISI_PTT_TRACE_BUF_SIZE) {
-		perf_aux_output_end(handle, buf->pos);
-
+	perf_aux_output_end(handle, size);
+	if (!stop) {
 		buf = perf_aux_output_begin(handle, event);
 		if (!buf)
 			return -EINVAL;