The size of a classical CAN frame is roughly 16 bytes, way less than
an USB packet (varies between devices but often between 64 and 512
bytes).
This es58x_netdev_queue_set_dql_min_limit() forces to do a bulk send
up to a threshold given by dql_min_limit in order to prevent sending
many small USB packets even when small burst occurs (BQL algorithm is
not able to immediately adjust dql.min_limit value).
Doing so increases the throughput with a minimum impact on the
latency: the time lost to stuff several frame in a single USB packet
is negligible compared to the gain of not having to send several USB
packets.
Co-developed-by: Arunachalam Santhanam <arunachalam.santhanam@xxxxxxxxxxxx>
Signed-off-by: Arunachalam Santhanam <arunachalam.santhanam@xxxxxxxxxxxx>
Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
---
Note: Contrary to previous version, the dql_min_limit field is not
guarded any more by #ifdef CONFIG_BQL: removing that field would
create a hole, so there is no gain to do so. If CONFIG_BQL is indeed
deactivated the field will just be unused.
---
drivers/net/can/usb/etas_es58x/es581_4.c | 2 ++
drivers/net/can/usb/etas_es58x/es58x_core.c | 5 ++++
drivers/net/can/usb/etas_es58x/es58x_core.h | 27 +++++++++++++++++++++
drivers/net/can/usb/etas_es58x/es58x_fd.c | 2 ++
4 files changed, 36 insertions(+)
diff --git a/drivers/net/can/usb/etas_es58x/es581_4.c b/drivers/net/can/usb/etas_es58x/es581_4.c
index a4b21dfd1bff..6b39d0cad7bb 100644
--- a/drivers/net/can/usb/etas_es58x/es581_4.c
+++ b/drivers/net/can/usb/etas_es58x/es581_4.c
@@ -481,6 +481,8 @@ const struct es58x_parameters es581_4_param = {
* unclear.
*/
.fifo_mask = 63, /* echo_skb_max = 64 */
+ /* Empirical value. */
+ .dql_min_limit = CAN_FRAME_LEN_MAX * 50,
.tx_bulk_max = ES581_4_TX_BULK_MAX,
.urb_cmd_header_len = ES581_4_URB_CMD_HEADER_LEN,
.rx_urb_max = ES58X_RX_URBS_MAX,
diff --git a/drivers/net/can/usb/etas_es58x/es58x_core.c b/drivers/net/can/usb/etas_es58x/es58x_core.c
index 7b9b993c0b5b..b07b9f085687 100644
--- a/drivers/net/can/usb/etas_es58x/es58x_core.c
+++ b/drivers/net/can/usb/etas_es58x/es58x_core.c
@@ -461,6 +461,8 @@ static void es58x_can_flush_echo_skb(struct net_device *netdev)
priv->tx_tail = 0;
priv->tx_head = 0;
netdev_reset_queue(netdev);
+ es58x_netdev_queue_set_dql_min_limit(netdev_get_tx_queue(netdev, 0),
+ priv->es58x_dev->param->dql_min_limit);
}
/**
@@ -2148,6 +2150,9 @@ static int es58x_init_netdev(struct es58x_device *es58x_dev, int channel_idx)
netdev_dbg(netdev, "%s: Registered channel %s\n",
es58x_dev->udev->product, netdev->name);
+ es58x_netdev_queue_set_dql_min_limit(netdev_get_tx_queue(netdev, 0),
+ es58x_dev->param->dql_min_limit);
+
return ret;
}
diff --git a/drivers/net/can/usb/etas_es58x/es58x_core.h b/drivers/net/can/usb/etas_es58x/es58x_core.h
index f0cf88a96816..086c17693f9a 100644
--- a/drivers/net/can/usb/etas_es58x/es58x_core.h
+++ b/drivers/net/can/usb/etas_es58x/es58x_core.h
@@ -276,6 +276,15 @@ struct es58x_priv {
* not exceed the maximum size of the device internal TX FIFO
* length. This parameter is used to control the network queue
* wake/stop logic.
+ * @dql_min_limit: Dynamic Queue Limits (DQL) absolute minimum limit
+ * of bytes allowed to be queued on this network device transmit
+ * queue. Used by the Byte Queue Limits (BQL) to determine how
+ * frequently the xmit_more flag will be set to true in
+ * es58x_start_xmit(). Set this value higher to optimize for
+ * throughput but be aware that it might have a negative impact
+ * on the latency! This value can also be set dynamically. Please
+ * refer to Documentation/ABI/testing/sysfs-class-net-queues for
+ * more details.
* @tx_bulk_max: Maximum number of TX messages that can be sent in one
* single URB packet.
* @urb_cmd_header_len: Length of the URB command header.
@@ -294,6 +303,7 @@ struct es58x_parameters {
u16 tx_urb_cmd_max_len;
u16 rx_urb_cmd_max_len;
u16 fifo_mask;
+ u16 dql_min_limit;
u8 tx_bulk_max;
u8 urb_cmd_header_len;
u8 rx_urb_max;
@@ -643,6 +653,23 @@ static inline enum es58x_flag es58x_get_flags(const struct sk_buff *skb)
return es58x_flags;
}
+/**
+ * es58x_netdev_queue_set_dql_min_limit - set dql minimum limit
+ * @q: pointer to transmit queue
+ * @min_limit: dql minimum limit
+ *
+ * Forces xmit_more() to return true until the minimum threshold
+ * defined by @min_limit is reached (or until the tx queue is
+ * empty).
+ */
+static inline void es58x_netdev_queue_set_dql_min_limit(struct netdev_queue *q,
+ unsigned int min_limit)
+{
+#ifdef CONFIG_BQL
+ q->dql.min_limit = min_limit;
+#endif
+}
+
int es58x_can_get_echo_skb(struct net_device *netdev, u32 packet_idx,
u64 *tstamps, unsigned int pkts);
int es58x_tx_ack_msg(struct net_device *netdev, u16 tx_free_entries,
diff --git a/drivers/net/can/usb/etas_es58x/es58x_fd.c b/drivers/net/can/usb/etas_es58x/es58x_fd.c
index a4e0867c9d4c..578a01580488 100644
--- a/drivers/net/can/usb/etas_es58x/es58x_fd.c
+++ b/drivers/net/can/usb/etas_es58x/es58x_fd.c
@@ -557,6 +557,8 @@ const struct es58x_parameters es58x_fd_param = {
* maximum, so no impact on performance was measured.
*/
.fifo_mask = 255, /* echo_skb_max = 256 */
+ /* Empirical value. */
+ .dql_min_limit = CAN_FRAME_LEN_MAX * 15,
.tx_bulk_max = ES58X_FD_TX_BULK_MAX,
.urb_cmd_header_len = ES58X_FD_URB_CMD_HEADER_LEN,
.rx_urb_max = ES58X_RX_URBS_MAX,
--
2.26.2
