usb: device: cdc_acm: send more than 1 byte in poll out
Schedule CDC ACM tx work to happen 1 ms after first unprocessed data
write. This gives enough leeway for the task writing to the queue to
write more than 1 byte before USB workqueue preempts and schedules IN
transfer. Sending more than 1 byte at a time increases data throughput
because transaction overhead remains the same regardless of packet size.
Prior to this change, virtually every IN transaction carried only one
character when CDC ACM was used as a console.
Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>
diff --git a/subsys/usb/device/class/cdc_acm.c b/subsys/usb/device/class/cdc_acm.c
index f28ae7d..0c269bd 100644
--- a/subsys/usb/device/class/cdc_acm.c
+++ b/subsys/usb/device/class/cdc_acm.c
@@ -96,7 +96,7 @@
#if defined(CONFIG_CDC_ACM_DTE_RATE_CALLBACK_SUPPORT)
cdc_dte_rate_callback_t rate_cb;
#endif
- struct k_work tx_work;
+ struct k_work_delayable tx_work;
/* Tx ready status. Signals when */
bool tx_ready;
bool rx_ready; /* Rx ready status */
@@ -218,7 +218,7 @@
return;
}
- k_work_submit_to_queue(&USB_WORK_Q, &dev_data->tx_work);
+ k_work_schedule_for_queue(&USB_WORK_Q, &dev_data->tx_work, K_NO_WAIT);
}
static void tx_work_handler(struct k_work *work)
@@ -477,7 +477,7 @@
dev, dev_data, dev->config, &cdc_acm_data_devlist);
k_work_init(&dev_data->cb_work, cdc_acm_irq_callback_work_handler);
- k_work_init(&dev_data->tx_work, tx_work_handler);
+ k_work_init_delayable(&dev_data->tx_work, tx_work_handler);
return ret;
}
@@ -513,7 +513,7 @@
LOG_WRN("Ring buffer full, drop %zd bytes", len - wrote);
}
- k_work_submit_to_queue(&USB_WORK_Q, &dev_data->tx_work);
+ k_work_schedule_for_queue(&USB_WORK_Q, &dev_data->tx_work, K_NO_WAIT);
/* Return written to ringbuf data len */
return wrote;
@@ -1016,7 +1016,11 @@
}
}
- k_work_submit_to_queue(&USB_WORK_Q, &dev_data->tx_work);
+ /* Schedule with minimal timeout to make it possible to send more than
+ * one byte per USB transfer. The latency increase is negligible while
+ * the increased throughput and reduced CPU usage is easily observable.
+ */
+ k_work_schedule_for_queue(&USB_WORK_Q, &dev_data->tx_work, K_MSEC(1));
}
static const struct uart_driver_api cdc_acm_driver_api = {
