[ovs-discuss] Questions about the OVS group table

[C C]

Ok, thanks!

Ben Pfaff <blp at ovn.org> 于2020年7月11日周六 上午9:45写道：

> Please don't drop the list.
>
> No, that's not it.  All the logic for hashing groups is in
> ofproto/ofproto-dpif-xlate.c.  Look around in there.
>
> On Sat, Jul 11, 2020 at 09:43:31AM +0800, C C wrote:
> > Thank you, but I would like to know more about the hashing process. Can
> you
> > tell me how the hashing process is implemented in the code? I found this
> > function in OVS code, and this is the hash function of group？
> > static struct hlist_head *vport_hash_bucket(const struct datapath *dp,
> >                         u16 port_no)
> > {
> >     return &dp->ports[port_no & (DP_VPORT_HASH_BUCKETS - 1)];
> > }
> >
> > Ben Pfaff <blp at ovn.org> 于2020年7月11日周六 上午12:21写道：
> >
> > > On Fri, Jul 10, 2020 at 03:10:04PM +0800, C C wrote:
> > > > Hello! I'm a student at USTC. I've been working on projects with OVS
> > > > recently. I want to know what hash function is used by default for
> group
> > > > select. For example, "ovs-ofctl -O OpenFlow15 add-group br0
> group_id=1,
> > > > type=select, selection_method=hash, fields=ip_src
> > > bucket=actions=output:1".
> > > > Where is this hash function in the OVS src-code? I hope you can
> solve my
> > > > problem. Thank you!
> > >
> > > The FAQ says:
> > >
> > > Q: How does OVS divide flows among buckets in an OpenFlow "select"
> group?
> > >
> > >     A: In Open vSwitch 2.3 and earlier, Open vSwitch used the
> destination
> > >     Ethernet address to choose a bucket in a select group.
> > >
> > >     Open vSwitch 2.4 and later by default hashes the source and
> destination
> > >     Ethernet address, VLAN ID, Ethernet type, IPv4/v6 source and
> > > destination
> > >     address and protocol, and for TCP and SCTP only, the source and
> > > destination
> > >     ports.  The hash is "symmetric", meaning that exchanging source and
> > >     destination addresses does not change the bucket selection.
> > >
> > >     Select groups in Open vSwitch 2.4 and later can be configured to
> use a
> > >     different hash function, using a Netronome extension to the
> OpenFlow
> > > 1.5+
> > >     group_mod message.  For more information, see
> > >     Documentation/group-selection-method-property.txt in the Open
> vSwitch
> > >     source tree.
> > >
>
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