On Sat 24 Oct 2020 at 20:40, Jamal Hadi Salim [off-list ref] wrote:

On 2020-10-23 8:48 a.m., Vlad Buslov wrote:

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On Thu 22 Oct 2020 at 17:05, Jamal Hadi Salim [off-list ref] wrote:

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On 2020-10-21 4:19 a.m., Vlad Buslov wrote:

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On Tue 20 Oct 2020 at 15:29, Jamal Hadi Salim [off-list ref] wrote:

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On 2020-10-19 11:18 a.m., Vlad Buslov wrote:
My worry is you have a very specific use case for your hardware or
maybe it is ovs - where counters are uniquely tied to filters and
there is no sharing. And possibly maybe only one counter can be tied
to a filter (was not sure if you could handle more than one action
in the terse from looking at the code).

OVS uses cookie to uniquely identify the flow and it does support
multiple actions per flow.

ok, so they use it like a flowid/classid to identify the flow.
In our use case the cookie stores all kinds of other state that
the controller can avoid to lookup after a query.
index otoh is universal i.e two different users can intepret it
per action tying it specific stats.
IOW: I dont think it replaces the index.
Do they set cookies on all actions in a flow?

AFAIK on only one action per flow.

To each their own i guess. Sounds like it is being used as flowid
entity.
We pack a lot of metaencoding into those cookies. And to us
a "service" is essentially a filter match folowed by a graph
of actions (which could cyclic).

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Cookie only consumes space in resulting netlink packet if used set the
cookie during action init. Otherwise, the cookie attribute is omitted.

True, but: I am wondering why it is even considered in when terseness
was a requirement (and index was left out).

There was several reasons for me to include it:

- As I wrote in previous email its TLV is only included in dump if user
   set the cookie. Users who don't use cookies don't lose any performance
   of terse dump.

- Including it didn't require any changes to tc_action_ops->dump() (like
   passing 'terse' flag or introducing dedicated terse_dump() callback)
   because it is processed in tcf_action_dump_1().

- OVS was the main use-case for us because it relies on filter dump for
   flow revalidation and uses cookie to identify the flows.

Which is fine - but it is a very ovs specific need.

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In our case we totally bypass filters to reduce the amount of data
crossing to user space (tc action ls). Theres still a lot of data
crossing which we could trim with a terse dump. All we are interested
in are stats. Another alternative is perhaps to introduce the index for
the direct dump.

What is the direct dump?

tc action ls ...
Like i said in our use cases to get the stats we just dumped the actions
we wanted. It is a lot less data than having the filter + actions.
And with your idea of terseness we can trim down further how much
data by removing all the action attributes coming back if we set TERSE
flag in such a request. But the index has to be there to make sense.

Yes, that makes sense. I guess introducing something like 'tc action -br
ls ..' mode implemented by means of existing terse flag + new 'also
output action index' flag would achieve that goal.

Right. There should be no interest in the cookie here at all. Maybe
it could be optional with a flag indication.
Have time to cook a patch? I'll taste/test it.

Patch to make cookie in filter terse dump optional? That would break
existing terse dump users that rely on it (OVS).

cheers,
jamal