Re: [dpdk-dev] [RFC 1/4] ethdev: claim device reset as async

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

> -----Original Message-----
> From: Kevin Traynor [mailto:ktraynor@redhat.com]
> Sent: Wednesday, August 8, 2018 7:15 PM
> To: Zhang, Qi Z <qi.z.zhang@intel.com>; thomas@monjalon.net; Ananyev,
> Konstantin <konstantin.ananyev@intel.com>; Doherty, Declan
> <declan.doherty@intel.com>; Yigit, Ferruh <ferruh.yigit@intel.com>
> Cc: dev@dpdk.org; Shelton, Benjamin H <benjamin.h.shelton@intel.com>;
> Vangati, Narender <narender.vangati@intel.com>; Xing, Beilei
> <beilei.xing@intel.com>; Lu, Wenzhuo <wenzhuo.lu@intel.com>;
> 0000-cover-letter.patch@dpdk.org
> Subject: Re: [dpdk-dev] [RFC 1/4] ethdev: claim device reset as async
> 
> On 08/08/2018 08:00 AM, Qi Zhang wrote:
> > rte_eth_dev_reset should be implemented in an async way since it is
> > possible 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, all these time consuming task will block the the
> > interrupt thread.
> > The patch claims rte_eth_dev_reset is an async function and introduce
> > a new event RTE_ETH_EVENT_RESET_COMPLETE. PMD should raise this
> event
> > when finish reset in background. The applicaiton should always wait
> > for this event before continue to configure and restart the device.
> >
> > Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>
> > ---
> >  lib/librte_ethdev/rte_ethdev.h | 48
> > ++++++++++++++++++++++++++----------------
> >  1 file changed, 30 insertions(+), 18 deletions(-)
> >
> > diff --git a/lib/librte_ethdev/rte_ethdev.h
> > b/lib/librte_ethdev/rte_ethdev.h index 7070e9ab4..541b5161d 100644
> > --- a/lib/librte_ethdev/rte_ethdev.h
> > +++ b/lib/librte_ethdev/rte_ethdev.h
> > @@ -1814,21 +1814,34 @@ 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.
> > + *
> > + * So we claimed rte_eth_dev_reset as an async API, 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.
> > + *
> > + * PMD is responsrible to implement ops->dev_reset in an async way,
> > + it can
> > + * offload the whole task into a separate thread, or maybe just
> > + pending on
> > + * hardware interrupt as reset dependency ready or start a timely
> > + alarm
> > + * to poll register status as a background daemon. PMD is also
> > + responsible
> > + * to raise the RTE_ETH_EVENT_RESET_COMPLETE event to notify the
> > + application
> > + * when reset is complete.
> > + *
> > + * Application should not assume device reset is finished after
> > + * rte_eth_dev_reset 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.
> > + *
> 
> If you intend to make this change for 18.11, 

It's not for 18.11, it's for 19.02, 

then I think you need to
> document it as part of 18.08. 

Yes I will send the API change notification in 18.11.