[ovs-dev] [PATCH] ofproto: Resubmit statistics improperly account during failover.

[Ethan Jackson]

I added the following paragraph to the commit message.

    Generally speaking, when a facet is facet_put__() into the
    datapath, the kernel returns the old flow's statistics so they may
    be accounted for in user space.  These statistics are generally
    pushed down to the relevant facet's resubmit children.  Before this
    patch, facet_put__() did not compensate for the fact that many of
    the statistics in the datapath may have been already pushed.
    Thus the entire packet count stored in the datapath would be pushed
    to its children instead of simply the packets which have accrued
    since the last accounting.  This patch fixes the behavior by
    subtracting already accounted for packets from the statistics
    returned by the datapath.

On Tue, May 3, 2011 at 12:42, Ben Pfaff <blp at nicira.com> wrote:
> On Mon, May 02, 2011 at 01:38:50PM -0700, Ethan Jackson wrote:
>> In some cases, when a facet's actions change because it resubmits
>> into a different rule.  It will account all packets it as accrued
>> in the datapath to the new rule.  Due to the algorithm we are
>> using, it is acceptable for a facet to miscount at most 1 second
>> worth of packets in this manor.  This patch implements the proper
>> behavior.
>
> The above commit message does a good job explaining the "why", but not
> the observable effect of the change.  I'm feeling really slow today,
> so would you mind walking me through what happens differently with
> this commit applied?
>
> Thanks,
>
> Ben.
>