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

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?

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Our assumptions so far had no such constraints.
Maybe a new TERSE_OPTIONS TLV, and then add an extra flag
to indicate interest in the tlv? Peharps store the stats in it as well.

Maybe, but wouldn't that require making it a new dump mode? Current
terse dump is already in released kernel and this seems like a
backward-incompatible change.

I meant you would set a new flag(in addition to TERSE) in a request to
the kernel to ask for the index to be made available on the response.
Response comes back in a TLV with just index in it for now.

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This wouldn't be much of a terse dump anymore. What prevents user that
needs all action info from calling regular dump? It is not like terse
dump substitutes it or somehow makes it harder to use.

Both scaling and correctness are important. You have the cookie
in the terse dump, thats a lot of data.

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).

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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.

cheers,
jamal