[ovs-discuss] Question regarding group reference count

Ben Pfaff blp at ovn.org
Fri Jul 7 15:45:20 UTC 2017


It's probably a bug in OVS.  The group reference count is, from an OVS
perspective, a bookkeeping exercise without real value, so it can easily
get out of sync.

On Thu, Jul 06, 2017 at 09:37:49PM +0000, Charles Chan wrote:
> Hi everyone,
> 
> I just downloaded the latest OVS release (2.7.1) but unfortunately I am
> still able to reproduce the issue.
> It seems to be an OVS-specific issue since the reference count is reported
> correctly on other OF-DPA based hardware switches.
> Any thought?
> 
> Thanks,
> Charles
> 
> On Mon, Jun 19, 2017 at 4:46 PM Charles Chan <charles at onlab.us> wrote:
> 
> > Hi everyone,
> >
> > I noticed a strange behavior of group reference count in ovs 2.7.0 and
> > therefore I am writing to confirm if this is expected.
> >
> > I created 2 indirect groups and 1 select group. There are 2 buckets in the
> > select group, each of them points to one of the indirect group.
> > sudo ovs-ofctl -O OpenFlow13 dump-groups ovs-br
> > OFPST_GROUP_DESC reply (OF1.3) (xid=0x2):
> > group_id=201,type=indirect,bucket=actions=output:1
> > group_id=202,type=indirect,bucket=actions=output:2
> > group_id=101,type=select,
> > *bucket=actions=group:201,bucket=actions=group:202*
> >
> > I also created a flow that points to the select group.
> > sudo ovs-ofctl -O OpenFlow13 dump-flows ovs-br
> > OFPST_FLOW reply (OF1.3) (xid=0x2):
> >  cookie=0x0, duration=31.409s, table=0, n_packets=0, n_bytes=0,
> > vlan_tci=0x000a/0x1fff actions=group:101
> >  cookie=0x0, duration=275.500s, table=0, n_packets=0, n_bytes=0,
> > priority=0 actions=NORMAL
> >
> > However, the reference count of these 2 indirect groups are both zero.
> > sudo ovs-ofctl -O OpenFlow13 dump-group-stats ovs-br
> > OFPST_GROUP reply (OF1.3) (xid=0x2):
> >  group_id=201,duration=185.249s,*ref_count=0*
> > ,packet_count=0,byte_count=0,bucket0:packet_count=0,byte_count=0
> >  group_id=202,duration=159.981s,*ref_count=0*
> > ,packet_count=0,byte_count=0,bucket0:packet_count=0,byte_count=0
> >
> >  group_id=101,duration=111.349s,ref_count=1,packet_count=0,byte_count=0,bucket0:packet_count=0,byte_count=0,bucket1:packet_count=0,byte_count=0
> >
> > I further looked up OF 1.3 spec and discovered this description in the
> > section of OFPMP_GROUP.
> > uint32_t ref_count; /* Number of *flows or groups that directly forward
> > to this group*. */
> > According to my interpretation of the spec, the reference count of these
> > indirect groups should both be 1 instead of 0 since they are referenced by
> > the select group.
> >
> > This can be easily reproduced by following steps.
> > sudo ovs-vsctl add-br ovs-br
> > sudo ovs-ofctl -O OpenFlow13 add-group ovs-br
> > group_id=201,type=indirect,bucket=actions=output:1
> > sudo ovs-ofctl -O OpenFlow13 add-group ovs-br
> > group_id=202,type=indirect,bucket=actions=output:2
> > sudo ovs-ofctl -O OpenFlow13 add-group ovs-br
> > group_id=101,type=select,bucket=actions=group:201,bucket=actions=group:202
> > sudo ovs-ofctl -O OpenFlow13 add-flow ovs-br vlan_vid=10,actions=group:101
> >
> > I installed OVS from the 2.7.0 tarball. This is the version I am using.
> > sudo ovs-vsctl --version
> > ovs-vsctl (Open vSwitch) 2.7.0
> > DB Schema 7.14.0
> >
> > Thanks,
> > Charles
> > --
> >
> > Charles Chan
> > Member of Technical Staff, ON.Lab
> > Member of Ambassador Steering Team, ONOS/CORD Community
> >
> -- 
> 
> Charles Chan
> Member of Technical Staff, ONF
> Member of Ambassador Steering Team, ONOS/CORD Community

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