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From: Pauli Virtanen <pav@iki.fi>
To: linux-bluetooth@vger.kernel.org
Cc: Pauli Virtanen <pav@iki.fi>
Subject: [PATCH BlueZ v2] client: fix ISO send data rate
Date: Sat, 11 May 2024 18:45:46 +0300
Message-ID: <30fd803be62f762706486698821e9e5fff2d0b63.1715442270.git.pav@iki.fi>
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We are sending data to controller at wrong average rate not equal to
1 packet / SDU interval, if Transport_Latency is not an integer multiple
of SDU_Interval.  The calculation currently may also give zero, so no
data gets sent.

We are sending data in bursts of num ~= Transport_Latency/SDU_Interval
packets, in hopes that possibly larger timer interval makes things more
efficient.

Fix the data rate by sending num packets every num*SDU_Interval, so that
the average data rate is correct.

Also fix use of itimerspect.it_value with TFD_TIMER_ABSTIME.  The value
set previously is going to always be in the past in CLOCK_MONOTONIC so
just set it to 1.
---

Notes:
    v2: Buffer one interval immediately as before.
    
    This assumes kernel shall set qos.interval to SDU_Interval and not
    ISO_Interval.

 client/player.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/client/player.c b/client/player.c
index 7f67425aa..df5cb8924 100644
--- a/client/player.c
+++ b/client/player.c
@@ -5066,21 +5066,30 @@ static int transport_send(struct transport *transport, int fd,
 	if (timer_fd < 0)
 		return -errno;
 
+	/* Send data in bursts of
+	 * num = ROUND_CLOSEST(Transport_Latency (ms) / SDU_Interval (us))
+	 * with average data rate = 1 packet / SDU_Interval
+	 */
+	transport->num = ROUND_CLOSEST(qos->latency * 1000, qos->interval);
+	if (!transport->num)
+		transport->num = 1;
+
 	memset(&ts, 0, sizeof(ts));
-	ts.it_value.tv_nsec = qos->latency * 1000000;
-	ts.it_interval.tv_nsec = qos->latency * 1000000;
+	ts.it_value.tv_nsec = 1;
+	ts.it_interval.tv_nsec = transport->num * qos->interval * 1000;
 
-	if (timerfd_settime(timer_fd, TFD_TIMER_ABSTIME, &ts, NULL) < 0)
+	if (timerfd_settime(timer_fd, TFD_TIMER_ABSTIME, &ts, NULL) < 0) {
+		close(timer_fd);
 		return -errno;
+	}
 
 	transport->fd = fd;
-	/* num of packets = ROUND_CLOSEST(latency (ms) / interval (us)) */
-	transport->num = ROUND_CLOSEST(qos->latency * 1000, qos->interval);
 	transport->timer_io = io_new(timer_fd);
 
 	io_set_read_handler(transport->timer_io, transport_timer_read,
 						transport, NULL);
 
+	/* One extra packet to buffers immediately */
 	return transport_send_seq(transport, fd, 1);
 }
 
-- 
2.45.0