Re: virtio "how to restart applications" - //dpdk.org/doc/virtio-net-pmd

[Gopakumar Choorakkot Edakkunni <gopakumar.c.e@gmail.com>]

Thanks again Yuanhan, you are the true expert!!

Rgds,
Gopa.

On Thu, Mar 16, 2017 at 10:40 PM, Yuanhan Liu <yuanhan.liu@linux.intel.com>
wrote:

> On Thu, Mar 16, 2017 at 10:30:09PM -0700, Gopakumar Choorakkot Edakkunni
> wrote:
> > Thanks for the confirmation, glad I reached the person who knows the
> nuts and
> > bolts of virtio :-). So if the host is not in our control (ie if I am
> just
> > running as a VM on host provided by thirdparty vendor), is there any
> workaround
> > I can do from the guest side to prevent problems from happening on a
> guest
> > restart ?
>
> Not too much. You might want to hack the guest DPDK EAL memory initiation
> part though, to not reset the hugepage memory on start. But that's too
> hacky
> that I will not recommend you to do so!
>
> > And if theres no workarounds at all and the host has to change, instead
> of
> > asking the third party vendor to do a wholesale upgrade to 16.04, is
> there one/
> > few commits that can be added to the host ovs-dpdk to take care of this
> guest
> > restart virtio-reset-before opening case ?
>
> Yes, backporting the commits I have mentioned should be able to fix it.
> But please note that I did some code refactorings before those fixes: it
> won't apply cleanly to DPDK v2.2.
>
> And if you want to upgrade, I'd suggest to upgrade to v16.11, which is
> LTS release.
>
>         --yliu
> >
> > Rgds,
> > Gopa.
> >
> > On Thu, Mar 16, 2017 at 10:24 PM, Yuanhan Liu <
> yuanhan.liu@linux.intel.com>
> > wrote:
> >
> >     On Thu, Mar 16, 2017 at 10:20:30PM -0700, Gopakumar Choorakkot
> Edakkunni
> >     wrote:
> >     > >> When I was saying dpdk version, I meant the DPDK version with
> OVS.
> >     >
> >     > Oh I see! My apologies for the misuderstanding. The dpdk version
> used by
> >     host
> >     > ovs should be dpdk2.2, the guest process uses dpdk16.07. The OVS
> process
> >     is not
> >     > getting restarted, what is getting restarted is the guest process
> using
> >     > dpdk16.07 - so the above clarifications you had about virtio being
> >     > reset-before-opened on guest restart - does that still hold good
> or does
> >     that
> >     > need the HOST side dpdk to be 16.04 or above ?
> >
> >     Yes, the HOST dpdk should be >= v16.04.
> >
> >             --yliu
> >     >
> >     > >> And yes, the fixes are not included in the DPDK required for
> OVS 2.4.
> >     >
> >     > Thanks for the info.
> >     >
> >     > Rgds,
> >     > Gopa.
> >     >
> >     > On Thu, Mar 16, 2017 at 10:13 PM, Yuanhan Liu <
> >     yuanhan.liu@linux.intel.com>
> >     > wrote:
> >     >
> >     >     On Thu, Mar 16, 2017 at 09:56:01PM -0700, Gopakumar Choorakkot
> >     Edakkunni
> >     >     wrote:
> >     >     > Hi Yuanhan,
> >     >     >
> >     >     > Thanks for the confirmation about not having to do anything
> special
> >     to
> >     >     close
> >     >     > the ports on dpdk going down or coming up.
> >     >     >
> >     >     > As for the question about if I met any issue of ovs getting
> stuck -
> >     yes,
> >     >     my
> >     >     > guest process runs dpdk 16.07 as I mentioned earlier - and
> if I
> >     kill my
> >     >     guest
> >     >     > process, then the host OVS-dpdk on the host reports stall !
> The
> >     OVS-dpdk
> >     >     and
> >     >     > emu versions I use are as below. But maybe that is because
> of the
> >     ovs
> >     >     missing
> >     >     > the fixes you mentioned ?
> >     >
> >     >     When I was saying dpdk version, I meant the DPDK version with
> OVS.
> >     >
> >     >     > ~# ovs-vswitchd --version
> >     >     > ovs-vswitchd (Open vSwitch) 2.4.1
> >     >
> >     >     And yes, the fixes are not included in the DPDK required for
> OVS 2.4.
> >     >
> >     >             --yliu
> >     >
> >     >     > Compiled Nov 14 2016 06:53:31
> >     >     > # kvm --version
> >     >     > QEMU emulator version 2.2.0, Copyright (c) 2003-2008 Fabrice
> >     Bellard
> >     >     > ~#
> >     >     >
> >     >     >
> >     >     > Rgds,
> >     >     > Gopa.
> >     >     >
> >     >     > On Thu, Mar 16, 2017 at 9:35 PM, Yuanhan Liu <
> >     yuanhan.liu@linux.intel.com
> >     >     >
> >     >     > wrote:
> >     >     >
> >     >     >     On Thu, Mar 16, 2017 at 07:48:28PM -0700, Gopakumar
> Choorakkot
> >     >     Edakkunni
> >     >     >     wrote:
> >     >     >     > Thanks a lot for the response Yuanhan. I am using dpdk
> >     v16.07. So
> >     >     what
> >     >     >     you are
> >     >     >     > saying is that in 16.07, we dont really need to call
> >     >     rte_eth_dev_close()
> >     >     >     on
> >     >     >     > exit,
> >     >     >
> >     >     >     It's not about "don't really need", it's more like "it's
> hard
> >     to".
> >     >     Just
> >     >     >     think that it may crash at any time.
> >     >     >
> >     >     >     > because dpdk will ensure that it will do virtio reset
> before
> >     init
> >     >     when it
> >     >     >     > comes up right ?
> >     >     >
> >     >     >     No, It just handles the abnormal case well when guest APP
> >     restarts.
> >     >     >
> >     >     >     > Regarding the vhost commits you mentioned - do we
> still need
> >     those
> >     >     fixes
> >     >     >     if we
> >     >     >     > have the "virtio reset before init" mechanism ?
> >     >     >
> >     >     >     Yes, we still need them: just think some malicious guest
> may
> >     also
> >     >     forge
> >     >     >     data like that.
> >     >     >
> >     >     >     I'm a bit confused then. Have you actually met any issue
> (like
> >     got
> >     >     stucked)
> >     >     >     with DPDK v16.07?
> >     >     >
> >     >     >             --yliu
> >     >     >
> >     >     >     > Or that is a seperate problem
> >     >     >     > altogether (and hence we would need those fixes) ?
> >     >     >     >
> >     >     >     > Rgds,
> >     >     >     > Gopa.
> >     >     >     >
> >     >     >     > On Thu, Mar 16, 2017 at 7:06 PM, Yuanhan Liu <
> >     >     yuanhan.liu@linux.intel.com
> >     >     >     >
> >     >     >     > wrote:
> >     >     >     >
> >     >     >     >     On Thu, Mar 16, 2017 at 12:39:16PM -0700, Gopakumar
> >     Choorakkot
> >     >     >     Edakkunni
> >     >     >     >     wrote:
> >     >     >     >     > So the doc says we should call
> rte_eth_dev_close()
> >     *before*
> >     >     going
> >     >     >     down.
> >     >     >     >     And I
> >     >     >     >     > know that especially in dpdk-virtionet  in the
> guest +
> >     >     ovs-dpdk in
> >     >     >     the
> >     >     >     >     host,
> >     >     >     >     > the ovs ends up getting stalled/stuck (!!) if I
> dont
> >     close
> >     >     the port
> >     >     >     >     before
> >     >     >     >     > starting() it when the guest dpdk process comes
> back
> >     up.
> >     >     >     >
> >     >     >     >     I'm assuming you were using an old version,
> something
> >     like dpdk
> >     >     v2.2?
> >     >     >     >     IIRC, DPDK v16.04 should have fixed your issue.
> >     >     >     >
> >     >     >     >     > Considering that this not done properly can
> screw up
> >     the HOST
> >     >     ovs,
> >     >     >     and I
> >     >     >     >     want
> >     >     >     >     > to do everything possible to avoid that, I want
> to be
> >     200%
> >     >     sure
> >     >     >     that I
> >     >     >     >     call
> >     >     >     >     > close even if my process gets a kill -9 .. So
> obviously
> >     the
> >     >     only
> >     >     >     way of
> >     >     >     >     doing
> >     >     >     >     > that is to close the port when the dpdk process
> comes
> >     back up
> >     >     and
> >     >     >     >     *before* we
> >     >     >     >     > init the port. rte_eth_dev_close() is not
> capable of
> >     doing
> >     >     that as
> >     >     >     it
> >     >     >     >     expects
> >     >     >     >     > the port parameters to be initialized etc..
> before it
> >     can be
> >     >     >     called.
> >     >     >     >
> >     >     >     >     We do virtio reset before init, which is basically
> what
> >     >     >     rte_eth_dev_close()
> >     >     >     >     mainly does. So I see no big issue here.
> >     >     >     >
> >     >     >     >     The stuck issue is due to hugepage reset by the
> guest
> >     DPDK
> >     >     >     application,
> >     >     >     >     leading all virtio vring elements being mem
> zeroed. The
> >     old
> >     >     vhost
> >     >     >     doesn't
> >     >     >     >     handle it well, as a result, it got stuck. And
> here are
> >     some
> >     >     relevant
> >     >     >     >     commits:
> >     >     >     >
> >     >     >     >         a436f53 vhost: avoid dead loop chain
> >     >     >     >         c687b0b vhost: check for ring descriptors
> overflow
> >     >     >     >         623bc47 vhost: do sanity check for ring
> descriptor
> >     length
> >     >     >     >
> >     >     >     >             --yliu
> >     >     >     >
> >     >     >     >     > Any other
> >     >     >     >     > suggestions on what can be done to close on
> restart
> >     rather
> >     >     than
> >     >     >     close on
> >     >     >     >     going
> >     >     >     >     > down ? Thought of bouncing this by the alias
> before I
> >     add a
> >     >     version
> >     >     >     of
> >     >     >     >     close
> >     >     >     >     > myself that can do this close-on-restart
> >     >     >     >
> >     >     >     >
> >     >     >
> >     >     >
> >     >
> >     >
> >
> >
>