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

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

On 10/4/2018 4:58 PM, Zhang, Qi Z wrote:
> 
> 
>> -----Original Message-----
>> From: Yigit, Ferruh
>> Sent: Thursday, October 4, 2018 7:30 PM
>> To: Zhang, Qi Z <qi.z.zhang@intel.com>; thomas@monjalon.net; Doherty,
>> Declan <declan.doherty@intel.com>
>> Cc: ktraynor@redhat.com; dev@dpdk.org; Shelton, Benjamin H
>> <benjamin.h.shelton@intel.com>; Vangati, Narender
>> <narender.vangati@intel.com>
>> Subject: Re: [RFC v3] ethdev: claim device reset as async
>>
>> 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.
> 
> I'd like to have this new state which represent the situation of the device more accurate.
> In this patch RTE_ETH_DEV_RESETTING is just to be used to prevent double reset, but in future it can also be used to prevent invalid operation during device reset.
> 
> Of cause we need to make sure it does not break exist behavior and seems add RTE_ETH_DEV_RESETTING check in rte_eth_find_next_owned_by and rte_eth_find_next is able to fix the issue you observed.
> 
> I can add this in v4 if you agree the idea.
> 
>>
>> <...>
>>
>>> @@ -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.
> 
> OK
> 
>>
>> 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.
> 
> Typically device reset happens when application receive RTE_ETH_EVENT_INTR_RESET and this is in interrupt thread. 
> Invoke an async API in interrupt thread is the right way, is it better if we highlight this is the only way?
> I may not prefer to expose the sync API right now, it's better to figure out some typical usage before we expose this, but so far I don't have.

Hi Qi,

Is the 'rte_eth_dev_reset_async()' still required? Is there any update planned
to this RFC?

> 
> Regards
> Qi
> 
> 
>>
>>> + *
>>> + * 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 */
>>>
>