linux-kernel - [PATCH v2 3/5] hwtracing: hisi_ptt: Optimize the trace data committing

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Date:   Thu, 14 Sep 2023 19:22:21 +0800
From:   Yicong Yang <yangyicong@...wei.com>
To:     <suzuki.poulose@....com>, <mathieu.poirier@...aro.org>,
        <jonathan.cameron@...wei.com>, <linux-kernel@...r.kernel.org>
CC:     <alexander.shishkin@...ux.intel.com>, <helgaas@...nel.org>,
        <linux-pci@...r.kernel.org>, <prime.zeng@...ilicon.com>,
        <linuxarm@...wei.com>, <yangyicong@...ilicon.com>,
        <hejunhao3@...wei.com>
Subject: [PATCH v2 3/5] hwtracing: hisi_ptt: Optimize the trace data committing

From: Yicong Yang <yangyicong@...ilicon.com>

Currently during the PTT trace, we'll only commit the data
to the perf core when its full, which means after 4 interrupts
and totally 16MiB data while the AUX buffer is 16MiB length.
Then the userspace gets notified and handle the data. The driver
cannot apply a new AUX buffer immediately until the committed data
are handled and there's enough room in the buffer again.

This patch tries to optimize this by commit the data in every
interrupts in a 4MiB granularity. Then the userspace can have
enough time to consume the data and there's always enough room
in the AUX buffer.

Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
---
 drivers/hwtracing/ptt/hisi_ptt.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/hwtracing/ptt/hisi_ptt.c b/drivers/hwtracing/ptt/hisi_ptt.c
index 3041238a6e54..4f355df8da23 100644
--- a/drivers/hwtracing/ptt/hisi_ptt.c
+++ b/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;
-- 
2.24.0