[ovs-dev] [PATCH 1/4] bfd: Implement BFD decay.

Alex Wang alexw at nicira.com
Mon Aug 5 22:56:35 UTC 2013


Thanks Ethan for the review.

I'll add 'in_decay' flag and set bfd->min_rx to decay_min_rx, when
receiving the FINAL packet.


On Mon, Aug 5, 2013 at 3:35 PM, Ethan Jackson <ethan at nicira.com> wrote:

> On Mon, Aug 5, 2013 at 2:04 PM, Alex Wang <alexw at nicira.com> wrote:
> > When there is no incoming data traffic at the interface for a period,
> > BFD decay allows the bfd session to increase the min_rx. This is
> > helpful in that some interfaces usually idle for long time. And cpu
> > consumption can be reduced by processing fewer bfd control
>
> "interaces usually" => "interfaces are usually" or "interfaces may be"
>
> "for long" => "for a long"
>
> There's one major issue with this patch.  In several places, it
> directly sets bfd->min_rx to either bfd->decay_min_rx or
> bfd->cfg_min_rx.  This is very much not allowed.  We have to give the
> remote BFD session a chance to react to the fact that we're changing
> our min_rx before we actually change it, otherwise it won't be sending
> control packets quickly enough and we'll have flaps.
>
> I think we should add a flag to in_decay which is set to true if decay
> mode has triggered and false if not. This line of code in bfd_poll()
> should change:
>
>      bfd->poll_min_rx = bfd->min_rx == bfd->decay_min_rx
>                            ? bfd->decay_min_rx : bfd->cfg_min_rx;
>
> to
>
> bfd->poll_min_rx = bfd->in_decay ? bfd->decay_min_rx
>     : bfd->cfg_min_rx
>
> Then whenever the configuration changes, or we move from in_decay =
> false to in_decay = true, we can call bfd_poll() and know that the
> transition to the new min_rx value will happen safely.  I think that
> would also simplify the patch quite a bit.
>
> Ethan
>
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