[dpdk-dev] [PATCH v6 1/4] lib/librte_ether: support device reset

[Lu, Wenzhuo]

Hi Jerin,

> -----Original Message-----
> From: Jerin Jacob [mailto:jerin.jacob at caviumnetworks.com]
> Sent: Wednesday, June 22, 2016 10:38 AM
> To: Lu, Wenzhuo
> Cc: Ananyev, Konstantin; Stephen Hemminger; dev at dpdk.org; Richardson,
> Bruce; Chen, Jing D; Liang, Cunming; Wu, Jingjing; Zhang, Helin;
> thomas.monjalon at 6wind.com
> Subject: Re: [dpdk-dev] [PATCH v6 1/4] lib/librte_ether: support device reset
> 
> On Wed, Jun 22, 2016 at 01:35:37AM +0000, Lu, Wenzhuo wrote:
> > Hi Jerin,
> >
> > > -----Original Message-----
> > > From: Jerin Jacob [mailto:jerin.jacob at caviumnetworks.com]
> > > Sent: Tuesday, June 21, 2016 10:29 PM
> > > To: Ananyev, Konstantin
> > > Cc: Lu, Wenzhuo; Stephen Hemminger; dev at dpdk.org; Richardson, Bruce;
> > > Chen, Jing D; Liang, Cunming; Wu, Jingjing; Zhang, Helin;
> > > thomas.monjalon at 6wind.com
> > > Subject: Re: [dpdk-dev] [PATCH v6 1/4] lib/librte_ether: support
> > > device reset
> > >
> > > On Tue, Jun 21, 2016 at 02:03:15PM +0000, Ananyev, Konstantin wrote:
> > > >
> > > >
> > > > > > > > > Hi Wenzhuo,
> > > > > > > > >
> > > > > > > > > > > > > > > On Mon, Jun 20, 2016 at 02:24:27PM +0800,
> > > > > > > > > > > > > > > Wenzhuo Lu
> > > wrote:
> > > > > > > > > > > > > > > > Add an API to reset the device.
> > > > > > > > > > > > > > > > It's for VF device in this scenario, kernel PF + DPDK VF.
> > > > > > > > > > > > > > > > When the PF port down->up, APP should call
> > > > > > > > > > > > > > > > this API to reset VF port. Most likely,
> > > > > > > > > > > > > > > > APP should call it in its management
> > > > > > > > > > > > > > > > thread and guarantee the thread safe. It
> > > > > > > > > > > > > > > > means APP should stop the rx/tx and the
> > > > > > > > > > > > > > > > device, then reset the device, then
> > > recover the device and rx/tx.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > Following is _a_ use-case for Device reset.
> > > > > > > > > > > > > > > But may be not be _the_ use case. IMO, We
> > > > > > > > > > > > > > > need to first say expected behavior of this
> > > > > > > > > > > > > > > API and add a use-case
> > > later.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > Other use-case would be, PCIe VF with
> > > > > > > > > > > > > > > functional level reset for SRIOV migration.
> > > > > > > > > > > > > > > Are we on same page?
> > > > > > > > > > > > > >
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > In my experience with Linux devices, this is
> > > > > > > > > > > > > > normally handled by the device driver in the
> > > > > > > > > > > > > > start routine.  Since any use case which needs
> > > > > > > > > > > > > > this is going to do a stop/reset/start
> > > > > > > > > > > > > > sequence, why not just have
> > > the VF device driver do this in the start routine?.
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > Adding yet another API and state transistion
> > > > > > > > > > > > > > if not necessary increases the complexity and
> > > > > > > > > > > > > > required test
> > > cases for all devices.
> > > > > > > > > > > > >
> > > > > > > > > > > > > I agree with Stephen here.I think if application
> > > > > > > > > > > > > needs to call start after the device reset then
> > > > > > > > > > > > > we could add this logic in start itself rather
> > > > > > > > > > > > > exposing a yet another API
> > > > > > > > > > > > Do you mean changing the device_start to include
> > > > > > > > > > > > all these actions, stop
> > > > > > > > > > > device -> stop queue -> re-setup queue -> start
> > > > > > > > > > > queue -> start
> > > device ?
> > > > > > > > > > >
> > > > > > > > > > > What was the expected API call sequence when you
> > > > > > > > > > > were
> > > introduced this API?
> > > > > > > > > > >
> > > > > > > > > > > Point was to have implicit device reset in the API
> > > > > > > > > > > call sequence(Wherever make sense for specific PMD)
> > > > > > > > > > I think the API call sequence depends on the
> > > > > > > > > > implementation of the APP. Let's say if there's not
> > > > > > > > > > this reset API, APP can use
> > > > > this
> > > > > > > API
> > > > > > > > > call sequence to handle the PF link down/up event,
> > > > > > > > > rte_eth_dev_close -> rte_eth_rx_queue_setup ->
> > > > > rte_eth_tx_queue_setup -
> > > > > > > >
> > > > > > > > > rte_eth_dev_start.
> > > > > > > > > > Actually our purpose is to use this reset API instead
> > > > > > > > > > of the API call sequence. You can see the reset API is
> > > > > > > > > > not necessary. The
> > > > > > > benefit
> > > > > > > > > is to save the code for APP.
> > > > > > > > >
> > > > > > > > > Then I am bit confused with original commit log description.
> > > > > > > > > |
> > > > > > > > > |It means APP should stop the rx/tx and the device, then
> > > > > > > > > |reset the device, then recover the device and rx/tx.
> > > > > > > > > |
> > > > > > > > > I was under impression that it a low level reset API for
> > > > > > > > > this device? Is n't it?
> > > > > > > > >
> > > > > > > > > The other issue is generalized outlook of the API,
> > > > > > > > > Certain PMD will not have PF link down/up event? Link
> > > > > > > > > down/up and only connected to VF and PF only for configuration.
> > > > > > > > >
> > > > > > > > > How about fixing it more transparently in PMD driver
> > > > > > > > > itself as PMD driver knows the PF link up/down event, Is
> > > > > > > > > it possible to recover the VF on that event if its only
> > > > > > > > > matter of resetting
> > > it?
> > > > > > > >
> > > > > > > > I think we already went through that discussion on the list.
> > > > > > > > Unfortunately with current dpdk design it is hardly possible.
> > > > > > > > To achieve that we need to introduce some sort of
> > > > > > > > synchronisation between IO and control APIs (locking or so).
> > > > > > > > Actually I am not sure why having a special reset function
> > > > > > > > will be a
> > > problem.
> > > > > > >
> > > > > > > |
> > > > > > > |It means APP should stop the rx/tx and the device, then
> > > > > > > |reset the device, then recover the device and rx/tx.
> > > > > > > |
> > > > > > > Just to understand, If application still need  to do the
> > > > > > > stop then what value addtion reset API brings on the table?
> > > > > >
> > > > > > If application calls dev_reset() it doesn't need to call dev_stop() before
> it.
> > > > > > dev_reset() will take care of it.
> > > > > > But it needs to make sure that no other thread will try to
> > > > > > modify that device state (either dev_stop/start, or
> > > > > > eth_rx_busrst/eth_tx_burst)
> > > while the reset op is in place.
> > > > >
> > > > > OK. This description looks different than commit log and API
> > > > > doxygen
> > > comment. Please fix it.
> > > > > How about a different name for this API. Device reset is too generic?
> > Any suggestion? I use this name because I believe what this API do is to reset
> the device.
> >
> > > > >
> > > > > >
> > > > > > >
> > > > > > >
> > > > > > > > Yes, it would exist only for VFs, for PF it could be left
> unimplemented.
> > > > > > > > Though it definitely seems more convenient from user point
> > > > > > > > of view, they would know: to handle VF reset event, they
> > > > > > > > just need to call that particular function, not to re-implement their
> own.
> > > > > > > What if driver returns "not implemented" then application
> > > > > > >will have do  generic rte_eth_dev_stop/rte_eth_dev_start.
> > > > > > >That way in application  perspective we are NOT solving any problem.
> > > > > >
> > > > > > True, but as I said for PF application would just never receive such event.
> > > > > What is this event ? Is it VF Link up/down event?
> > > > >
> > > > > No I was referring to VF itself, Other VF PMD drivers in
> > > > > drivers/net where this callback is not implemented.
> > > >
> > > > Hmm, the only suggestion I have here - Maintainers/developers of
> > > > non-Intel PMD will implement it for their VFs?
> > >
> > > That's fine. But, We have to know what to implement here in PMD
> perspective?
> > > That's reason being asking about the API expectation and application
> > > usage :-)
> > >
> > > > In case of course they do need to handle similar event.
> > > Which is this event and How application get notify it.
> > When the PF link is down/up, the PF will use the mailbox to send a message to
> VF. The event here means the VF receives that message from PF. So VF can know
> the physical link state changed. You see it's only for VF. PF will not receive such
> kind of message.
> > And we use the callback mechanism to let APP notified. APP should register a
> callback function. When VF driver receives the message it will call the callback
> function, then APP can know that.
> 
> How about the standardizing  a name for that event like
> RTE_ETH_EVENT_INTR_DOWNSTREAM_LSC or RTE_ETH_EVENT_INTR_PF_LSC
> or similar (like RTE_ETH_EVENT_INTR_RESET) and counter API in VF to handle
> the specific event whose API name similar to selected event name not
> eth_dev_reset(reset sounds like more like HW reset, In PCIe device perspective
> FLR etc)
> 
> OR
> 
> How about handling in more generic way where a generic alert message send by
> PF to VF like RTE_ETH_EVENT_INTR_PF_ALERT or similar.
> And have only one handle functions in VF side so that in future we can keep
> adding new functionality with out introducing new counter API in VF
> 
> Jerin
Lost here. I think these RTE_ETH_EVENTs are used to connect the APP call back functions with the events.
Actually I want the APP to register a callback function reset_event_callback for the reset event. Like this,
		/* register reset interrupt callback */
		rte_eth_dev_callback_register(portid,
			RTE_ETH_EVENT_INTR_RESET, reset_event_callback, NULL);
And when the VF driver finds PF link down/up, it  should  use _rte_eth_dev_callback_process(dev, RTE_ETH_EVENT_INTR_RESET) to run into the callback which is provided by APP. Means reset_event_callback here.

> 
> >
> > >
> > > > if not I suppose there is no harm to left it unimplemented.
> > > OK. If it is for VF/PF link down-up event then I will make it as 'nop'.
> > As explained above, the event is not VF/PF link down-up. Actually it's that VF is
> notified the PF link is down-up.
> >
> > And to my opinion, although now we only implement the reset API for VF, I
> believe there's nothing preventing us to implement this API for PF if we can find
> some scenario that we need to reset the PF link. The reset API is reset API, it can
> be used for the event described above. But it's not bound to this event.
> > >
> > > Jerin
> > >
> > > > Konstantin
> > > >