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

["Zhang, Qi Z" <qi.z.zhang@intel.com>]

> -----Original Message-----
> From: Yigit, Ferruh
> Sent: Tuesday, March 19, 2019 9:14 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 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?

Yes, I think the requirement is still there. Just don't have bandwidth work on this recently.
May I send out v1 for 19.05 in this week? since deprecation notes already be send out in 19.02 cycle


> 
> >
> > 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 */
> >>>
> >