Re: [dpdk-dev] [RFC v3] ethdev: claim device reset as async

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 9/20/2018 5:56 AM, Qi Zhang wrote:
> Device reset should be implemented in an async way since it is
> possible to be invoked in interrupt thread and sometimes to reset a
> device need to wait for some dependency, for example, a VF expects for
> PF ready or a NIC function as part of a SOC wait for the whole system
> reset complete, and all these time-consuming tasks will block the
> interrupt thread.
> The patch rename rte_eth_dev_reset to rte_eth_dev_reset_async and
> rework the implementation. It will spawn a new thread which will call
> ops->dev_reset, and when finished it will raise the event
> RTE_ETH_EVENT_RESET_COMPLETE. The application should always wait for
> this event before it continues to configure and restart the device.
> 
> Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>

<...>

> @@ -1385,10 +1413,26 @@ rte_eth_dev_reset(uint16_t port_id)
>  
>  	RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->dev_reset, -ENOTSUP);
>  
> +	/* already on resetting */
> +	if (dev->state == RTE_ETH_DEV_RESETTING)
> +		return 0;
> +
> +	args = calloc(1, sizeof(struct dev_reset_args));
> +	if (!args)
> +		return -ENOMEM;
> +
>  	rte_eth_dev_stop(port_id);
> -	ret = dev->dev_ops->dev_reset(dev);
>  
> -	return eth_err(port_id, ret);
> +	/* store previous device state temporary */
> +	args->pre_state = dev->state;
> +
> +	dev->state = RTE_ETH_DEV_RESETTING;

Do we need to update the state, I think this will break rte_eth_dev_count() and
friends, like during device reset app will think it has one less device in system.

<...>

> @@ -1814,21 +1816,29 @@ void rte_eth_dev_close(uint16_t port_id);
>   * RTE_ETH_EVENT_INTR_RESET event is detected, but can also use it to start
>   * a port reset in other circumstances.
>   *
> - * When this function is called, it first stops the port and then calls the
> - * PMD specific dev_uninit( ) and dev_init( ) to return the port to initial
> - * state, in which no Tx and Rx queues are setup, as if the port has been
> - * reset and not started. The port keeps the port id it had before the
> - * function call.
> - *
> - * After calling rte_eth_dev_reset( ), the application should use
> - * rte_eth_dev_configure( ), rte_eth_rx_queue_setup( ),
> - * rte_eth_tx_queue_setup( ), and rte_eth_dev_start( )
> - * to reconfigure the device as appropriate.
> - *
> - * Note: To avoid unexpected behavior, the application should stop calling
> - * Tx and Rx functions before calling rte_eth_dev_reset( ). For thread
> - * safety, all these controlling functions should be called from the same
> - * thread.
> + * @note
> + * Device reset may have the dependency, for example, a VF reset expects
> + * PF ready, or a NIC function as a part of a SOC need to wait for other
> + * parts of the system be ready, these are time-consuming tasks and will
> + * block current thread.
> + *
> + * As the name, rte_eth_dev_reset_async is an async API, it will spwan a
> + * new thread to call ops->dev_reset, once it is finished, it will raise
> + * the RTE_ETH_EVENT_RESET_COMPLETE event to notify application.  That makes
> + * things easy for an application that what to reset the device from the
> + * interrupt thread since typically a RTE_ETH_EVENT_INTR_RESET handler is
> + * invoked in interrupt thread.

thread calls dev_ops->dev_reset(dev) and wait for it, so it means
dev_ops->dev_reset is synchronous, perhaps it would be good to highlight this in
"dev_reset" comment to help PMD developers.

of dev_ops->dev_reset() is synchronous, means existing rte_eth_dev_reset() is
synchronous, so what do you thinks keep rte_eth_dev_reset() as it is and add new
rte_eth_dev_reset_async() API? Than we will have both sync and async solution.

> + *
> + * Application should not assume device reset is finished after
> + * rte_eth_dev_reset_async return, it should always wait for a
> + * RTE_ETH_EVENT_RESET_COMPLETE event and check the reset result.
> + * If reset success, application should call rte_eth_dev_configure( ),
> + * rte_eth_rx_queue_setup( ), rte_eth_tx_queue_setup( ),
> + * and rte_eth_dev_start( ) to reconfigure the device as appropriate.
> + *
> + * @Note
> + * To avoid unexpected behavior, the application should stop calling
> + * Tx and Rx functions before calling rte_eth_dev_reset_async( ).
>   *
>   * @param port_id
>   *   The port identifier of the Ethernet device.
> @@ -1837,12 +1847,10 @@ void rte_eth_dev_close(uint16_t port_id);
>   *   - (0) if successful.
>   *   - (-EINVAL) if port identifier is invalid.
>   *   - (-ENOTSUP) if hardware doesn't support this function.
> - *   - (-EPERM) if not ran from the primary process.
> - *   - (-EIO) if re-initialisation failed or device is removed.
>   *   - (-ENOMEM) if the reset failed due to OOM.
> - *   - (-EAGAIN) if the reset temporarily failed and should be retried later.
> + *   - (<0) other errors from low level driver.
>   */
> -int rte_eth_dev_reset(uint16_t port_id);
> +int rte_eth_dev_reset_async(uint16_t port_id);
>  
>  /**
>   * Enable receipt in promiscuous mode for an Ethernet device.
> @@ -2574,6 +2582,8 @@ enum rte_eth_event_type {
>  				/**< queue state event (enabled/disabled) */
>  	RTE_ETH_EVENT_INTR_RESET,
>  			/**< reset interrupt event, sent to VF on PF reset */
> +	RTE_ETH_EVENT_RESET_COMPLETE,
> +			/**< inform application that reset is completed */
>  	RTE_ETH_EVENT_VF_MBOX,  /**< message from the VF received by PF */
>  	RTE_ETH_EVENT_MACSEC,   /**< MACsec offload related event */
>  	RTE_ETH_EVENT_INTR_RMV, /**< device removal event */
>