[dpdk-dev] [PATCH v3 7/7] app/testpmd: adjust ethdev port ownership

[Matan Azrad]

Hi 
From: Ananyev, Konstantin [mailto:konstantin.ananyev at intel.com]
> Hi lads,
> 
> >
> > Hi Matan,
> >
> > On Fri, Jan 19, 2018 at 01:35:10PM +0000, Matan Azrad wrote:
> > > Hi Konstantin
> > >
> > > From: Ananyev, Konstantin, Friday, January 19, 2018 3:09 PM
> > > > > -----Original Message-----
> > > > > From: Matan Azrad [mailto:matan at mellanox.com]
> > > > > Sent: Friday, January 19, 2018 12:52 PM
> > > > > To: Ananyev, Konstantin <konstantin.ananyev at intel.com>; Thomas
> > > > > Monjalon <thomas at monjalon.net>; Gaetan Rivet
> > > > <gaetan.rivet at 6wind.com>;
> > > > > Wu, Jingjing <jingjing.wu at intel.com>
> > > > > Cc: dev at dpdk.org; Neil Horman <nhorman at tuxdriver.com>;
> > > > > Richardson, Bruce <bruce.richardson at intel.com>
> > > > > Subject: RE: [PATCH v3 7/7] app/testpmd: adjust ethdev port
> > > > > ownership
> > > > >
> > > > > Hi Konstantin
> > > > >
> > > > > From: Ananyev, Konstantin, Friday, January 19, 2018 2:38 PM
> > > > > > To: Matan Azrad <matan at mellanox.com>; Thomas Monjalon
> > > > > > <thomas at monjalon.net>; Gaetan Rivet
> <gaetan.rivet at 6wind.com>;
> > > > Wu,
> > > > > > Jingjing <jingjing.wu at intel.com>
> > > > > > Cc: dev at dpdk.org; Neil Horman <nhorman at tuxdriver.com>;
> > > > > > Richardson, Bruce <bruce.richardson at intel.com>
> > > > > > Subject: RE: [PATCH v3 7/7] app/testpmd: adjust ethdev port
> > > > > > ownership
> > > > > >
> > > > > > Hi Matan,
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Matan Azrad [mailto:matan at mellanox.com]
> > > > > > > Sent: Thursday, January 18, 2018 4:35 PM
> > > > > > > To: Thomas Monjalon <thomas at monjalon.net>; Gaetan Rivet
> > > > > > > <gaetan.rivet at 6wind.com>; Wu, Jingjing
> > > > > > > <jingjing.wu at intel.com>
> > > > > > > Cc: dev at dpdk.org; Neil Horman <nhorman at tuxdriver.com>;
> > > > Richardson,
> > > > > > > Bruce <bruce.richardson at intel.com>; Ananyev, Konstantin
> > > > > > > <konstantin.ananyev at intel.com>
> > > > > > > Subject: [PATCH v3 7/7] app/testpmd: adjust ethdev port
> > > > > > > ownership
> > > > > > >
> > > > > > > Testpmd should not use ethdev ports which are managed by
> > > > > > > other DPDK entities.
> > > > > > >
> > > > > > > Set Testpmd ownership to each port which is not used by
> > > > > > > other entity and prevent any usage of ethdev ports which are
> > > > > > > not owned by
> > > > Testpmd.
> > > > > > >
> > > > > > > Signed-off-by: Matan Azrad <matan at mellanox.com>
> > > > > > > ---
> > > > > > >  app/test-pmd/cmdline.c      | 89 +++++++++++++++++++----------
> -------
> > > > ----
> > > > > > -----
> > > > > > >  app/test-pmd/cmdline_flow.c |  2 +-
> > > > > > >  app/test-pmd/config.c       | 37 ++++++++++---------
> > > > > > >  app/test-pmd/parameters.c   |  4 +-
> > > > > > >  app/test-pmd/testpmd.c      | 63 ++++++++++++++++++++--------
> ----
> > > > > > >  app/test-pmd/testpmd.h      |  3 ++
> > > > > > >  6 files changed, 103 insertions(+), 95 deletions(-)
> > > > > > >
> > > > > > > diff --git a/app/test-pmd/cmdline.c b/app/test-pmd/cmdline.c
> > > > > > > index
> > > > > > > 31919ba..6199c64 100644
> > > > > > > --- a/app/test-pmd/cmdline.c
> > > > > > > +++ b/app/test-pmd/cmdline.c
> > > > > > > @@ -1394,7 +1394,7 @@ struct cmd_config_speed_all {
> > > > > > >  			&link_speed) < 0)
> > > > > > >  		return;
> > > > > > >
> > > > > > > -	RTE_ETH_FOREACH_DEV(pid) {
> > > > > > > +	RTE_ETH_FOREACH_DEV_OWNED_BY(pid, my_owner.id) {
> > > > > >
> > > > > > Why do we need all these changes?
> > > > > > As I understand you changed definition of
> > > > > > RTE_ETH_FOREACH_DEV(), so no testpmd should work ok default
> (no_owner case).
> > > > > > Am I missing something here?
> > > > >
> > > > > Now, After Gaetan suggestion RTE_ETH_FOREACH_DEV(pid) will
> > > > > iterate
> > > > over all valid and ownerless ports.
> > > >
> > > > Yes.
> > > >
> > > > > Here Testpmd wants to iterate over its owned ports.
> > > >
> > > > Why? Why it can't just iterate over all valid and ownerless ports?
> > > > As I understand it would be enough to fix current problems and
> > > > would allow us to avoid any changes in testmpd (which I think is a good
> thing).
> > >
> > > Yes, I understand that this big change is very daunted, But I think
> > > the current a lot of bugs in testpmd(regarding port ownership) even
> > > more
> > daunted.
> > >
> > > Look,
> > > Testpmd initiates some of its internal databases depends on specific
> > > port iteration, In some time someone may take ownership of Testpmd
> ports and testpmd will continue to touch them.
> 
> But if someone will take the ownership (assign new owner_id) that port will
> not appear in RTE_ETH_FOREACH_DEV() any more.
> 

Yes, but testpmd sometimes depends on previous iteration using internal database.
So it uses internal database that was updated by old iteration.  

> > >
> >
> > If I look back on the fail-safe, its sole purpose is to have seamless
> > hotplug with existing applications.
> >
> > Port ownership is a genericization of some functions introduced by the
> > fail-safe, that could structure DPDK further. It should allow
> > applications to have a seamless integration with subsystems using port
> > ownership. Without this, port ownership cannot be used.
> >
> > Testpmd should be fixed, but follow the most common design patterns of
> > DPDK applications. Going with port ownership seems like a paradigm
> > shift.
> >
> > > In addition
> > > Using the old iterator in some places in testpmd will cause a race for run-
> time new ports(can be created by failsafe or any hotplug code):
> > > - testpmd finds an ownerless port(just now created) by the old
> > > iterator and start traffic there,
> > > - failsafe takes ownership of this new port and start traffic there.
> > > Problem!
> 
> Could you shed a bit more light here - it would be race condition between
> whom and whom?

Sure.

> As I remember in testpmd all control ops are done within one thread (main
> lcore).

But other dpdk entity can use another thread, for example:
Failsafe uses the host thread(using alarm callback) to create a new port and to take ownership of a port.

The race:
Testpmd iterates over all ports by the master thread.
Failsafe takes ownership of a port by the host thread and start using it. 
=> The two dpdk entities may use the device at same time!

Obeying the new ownership rules can prevent all these races.

> The only way to attach/detach port with it - invoke testpmd CLI
> "attach/detach" port.
> 
> Konstantin
> 
> >
> > Testpmd does not handle detection of new port. If it did, testing
> > fail-safe with it would be wrong.
> >
> > At startup, RTE_ETH_FOREACH_DEV already fixed the issue of registering
> > DEFERRED ports. There are still remaining issues regarding this, but I
> > think they should be fixed. The architecture does not need to be
> > completely moved to port ownership.
> >
> > If anything, this should serve as a test for your API with common
> > applications. I think you'd prefer to know and debug with testpmd
> > instead of firing up VPP or something like that to determine what went
> > wrong with using the fail-safe.
> >
> > >
> > > In addition
> > > As a good example for well-done application (free from ownership
> > > bugs) I tried here to adjust Tespmd to the new rules and BTW to fix
> > > a
> > lot of bugs.
> >
> > Testpmd has too much cruft, it won't ever be a good example of a
> > well-done application.
> >
> > If you want to demonstrate ownership, I think you should start an
> > example application demonstrating race conditions and their mitigation.
> >
> > I think that would be interesting for many DPDK users.
> >
> > >
> > >
> > > So actually applications which are not aware to the port ownership
> > > still are exposed to races, but if there use the old iterator(with
> > > the new
> > change) the amount of races decreases.
> > >
> > > Thanks, Matan.
> > > > Konstantin
> > > >
> > > > >
> > > > > I added to Testpmd ability to take an ownership of ports as the
> > > > > new ownership and synchronization rules suggested, Since Tespmd
> > > > > is a DPDK entity which wants that no one will touch its owned
> > > > > ports, It must allocate
> > > > an unique ID, set owner for its ports (see in main function) and
> > > > recognizes them by its owner ID.
> > > > >
> > > > > > Konstantin
> > > > > >
> >
> > Regards,
> > --
> > Gaëtan Rivet
> > 6WIND