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usb: device: cdc_acm: send more than 1 byte in poll out

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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>
This commit is contained in:
Tomasz Moń 2022-12-13 11:24:05 +01:00 committed by Carles Cufí
parent 95717520bf
commit fed6bde788
1 changed files with 9 additions and 5 deletions
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14
subsys/usb/device/class/cdc_acm.c
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@ -96,7 +96,7 @@ struct cdc_acm_dev_data_t {
#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 @@ static void cdc_acm_write_cb(uint8_t ep, int size, void *priv)
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 @@ static int cdc_acm_init(const struct device *dev)
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 @@ static int cdc_acm_fifo_fill(const struct device *dev,
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 @@ static void cdc_acm_poll_out(const struct device *dev, unsigned char c)
}
}
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 = {