Re: [PATCH v6 0/4] support reset of VF link

[Luca Boccassi <lboccass@Brocade.com>]

On Fri, 2016-07-08 at 00:14 +0000, Lu, Wenzhuo wrote:
> > > > > > > > > > Hello Wenzhuo,
> > > > > > > > > >
> > > > > > > > > > I'm testing this patchset, but I am sporadically running
> > > > > > > > > > into an issue where the VFs reset fails after the PF flaps.
> > > > > > > > > >
> > > > > > > > > > I have a VM running on a KVM box with a X540-AT2, passing 2 VFs
> > in.
> > > > > > > > > >
> > > > > > > > > > I am using calling rte_eth_dev_reset in response to a
> > > > > > > > > > RTE_ETH_EVENT_INTR_RESET callback, and the following
> > > > > > > > > > errors appear in the
> > > > > > > > > > log:
> > > > > > > > > >
> > > > > > > > > > PMD: ixgbevf_dev_reset(): Ixgbe VF reset: Failed to update link.
> > > > > > > > > > PMD: ixgbe_alloc_rx_queue_mbufs(): RX mbuf alloc failed
> > > > > > > > > > queue_id=0
> > > > > > > > > > PMD: ixgbevf_dev_start(): Unable to initialize RX
> > > > > > > > > > hardware
> > > > > > > > > > (-12)
> > > > > > > > > > PMD: ixgbevf_dev_reset(): Ixgbe VF reset: Failed to start device.
> > > > > > > > > >
> > > > > > > > > > Jumping in with GDB, it seems that the rte_rxmbuf_alloc
> > > > > > > > > > call in ixgbe_alloc_rx_queue_mbufs returns NULL at
> > > > > > > > > > iteration 64 out of
> > > > 2048.
> > > > > > > > > > The application has ~500 2MB hugepages, and there's 2GB
> > > > > > > > > > of free memory available on top of that.
> > > > > > > > > >
> > > > > > > > > > Have you seen this before? Any pointer or suggestion for
> > debugging?
> > > > > > > > > >
> > > > > > > > > > Thanks!
> > > > > > > > > >
> > > > > > > > > > --
> > > > > > > > > > Kind regards,
> > > > > > > > > > Luca Boccassi
> > > > > > > > > I think the problem is the mbuf occupied by the packets is
> > > > > > > > > not released. This
> > > > > > > > memory has to be released by the APP, so my patches haven’t
> > > > > > > > covered
> > > > this.
> > > > > > > > Actually an example is needed to show how to use the reset API.
> > > > > > > > I plan to modify the testpmd.
> > > > > > > > > You may notice this feature is postponed to 16.11. Would
> > > > > > > > > you like to wait for
> > > > > > > > the new version that will include an example?
> > > > > > > >
> > > > > > > > Hi,
> > > > > > > >
> > > > > > > > Unfortunately we need the VF reset working sooner than that,
> > > > > > > > so one way or the other I'll need to sort it out. Given I've
> > > > > > > > got a use case where this is happening, if it can be helpful
> > > > > > > > for you I'm more than happy to help as a guinea pig. If you
> > > > > > > > could please give some guidance/guidelines with regards to
> > > > > > > > which API to use to sort the mbuf
> > > > > > problem, I can try it out and give back some feedback.
> > > > > > > >
> > > > > > > > Thanks!
> > > > > > > I made a stupid mistake and deleted all my code. So, I have to
> > > > > > > take some time to rewrite it :( Attached the example I used to
> > > > > > > test the reset API. It's
> > > > > > modified from the l2fwd example. So you can compare it with
> > > > > > l2fwd to see what need to be added.
> > > > > > > Hopefully it can help :)
> > > > > >
> > > > > > Thanks! That made me understand a couple of things more, and
> > > > > > I've got past the problem.
> > > > > >
> > > > > > Unfortunately now there's a bigger issue - rte_eth_dev_reset is
> > > > > > a blocking
> > > > call.
> > > > > > the _RESET event callback is fired when the PF goes down, but
> > > > > > when I call rte_eth_dev_reset it will block until the PF goes back up.
> > > > > > There is no way, as far as I can see, to know if the PF is back
> > > > > > up before
> > > > calling rte_eth_dev_reset.
> > > > > >
> > > > > > This is a problem because, as far as I understand, I have to
> > > > > > call all the rte_eth_dev_ APIs from the same thread, in my case
> > > > > > the master thread, and I can't have that block potentially indefinitely.
> > > > > >
> > > > > > Would it be possible to have 2 events instead of 1, one when the
> > > > > > PF goes down and one when it goes up? This way an application
> > > > > > would be able to soft-stop the port (drain queues, etc) when the
> > > > > > PF is down, and then call the reset API when it goes back up.
> > > > > >
> > > > > > Thanks!
> > > > > Sorry we cannot have 2 events now. There're 2 problems to have 2 events.
> > > > > 1, Normally we use kernel driver for PF. Now the kernel driver
> > > > > only have one
> > > > kind of message for link down and up. So we cannot tell if it's down or up.
> > > > > 2, When the PF is down, if we don't reset the VF, VF is not working.
> > > > > It cannot receive any message from PF. So we cannot know that when
> > > > > PF is up. It means normally we have to reset VF twice when PF down
> > > > > and up. (Surely we can wait a while when we receive the message
> > > > > from PF until PF is up. But we cannot tell how long the time is appropriate.
> > > > > So this *wait a while* may work for flash.)
> > > >
> > > > Thanks for the clarification, I understand.
> > > >
> > > > The problem with a blocking call is that we basically need to spawn
> > > > one thread per rte_eth_dev_reset call, since there is no way of
> > > > knowing if a PF is down for good or just flapping, and we can't have
> > > > a single thread managing all the interfaces being blocked forever
> > > > (EG: PF 1 and 2 go down, thread blocks on PF 1 reset call but it
> > > > never returns, meanwhile PF 2 goes back up but call is never made).
> > > >
> > > > A colleague of mine, Eric Kinzie, suggested to add a blocking
> > > > boolean parameter to rte_eth_dev_reset API. If set to false, then
> > > > the call will not block and just does one try and return an error (EAGAIN ?).
> > Would this be an acceptable proposition?
> > > It's a good suggestion.
> > > And I think if the parameter is set to false and the link is not up after trying
> > once, it will be APP's responsibility to setup a timer or something like that to
> > keep trying to bring up the link.
> > 
> > That seems reasonable. I've thrown together a quick diff and played with it on
> > top of your patches and DPDK 2.2, seems to work as intended, I'm attaching it
> > for reference. Feel free to pick it up, adapt it or ignore it :-)
> > 
> > Also I've noticed that the ixgbe is the only one that actually blocks,
> > e1000 returns already immediately if the dev_start fails (perhaps it should be
> > changed to be consistent?) and ixgb40 does weird things that I'm not sure about,
> > but couldn't spot a loop in there :-)
> > 
> > Also I've used int instead of bool because
> > drivers/net/e1000/base/e1000_osdep.h redefines bool and true/false, so
> > compilation fails when including stdbool.h and using bool in rte_ethdev.h
> > 
> > --
> > Kind regards,
> > Luca Boccassi
> Glad to know it's working now.  Thanks for your patch.  Surely I'll try to include it in the next version :)

Great, thanks!

Unfortunately I found one issue: if PF is down, and then the VF on the
guest is down as well (ip link down) and then goes back up before the
PF, then calling rte_eth_dev_reset will return 0 (success), even though
the PF is still down and it should fail. This is with ixgbe. Any idea
what could be the problem?

-- 
Kind regards,
Luca Boccassi