On 21 Jun 2024, at 10:00, Adrián Moreno wrote:
> On Thu, Jun 20, 2024 at 02:20:53PM GMT, Eelco Chaudron wrote:
>>
>>
>> On 5 Jun 2024, at 22:23, Adrian Moreno wrote:
>>
>>> (Was: Add psample support to NXAST_SAMPLE action)
>>>
>>> This is the userspace counterpart of the work being done in the kernel
>>> [1] which is still not merged (hence the RFC state). There, a new
>>> datapath action is added, called "emit_sample". Being a specific
>>> action, it promises a more efficient way of making packet samples
>>> available to observability applications.
>>>
>>> From the PoV of ovs-vswitchd, this new action is used to implement
>>> "local sampling". Local sampling (or lsample for short) is configured
>>> in a similar way as current per-flow IPFIX sampling, i.e: using the
>>> Flow_Sample_Collector_Set table and the NXAST_SAMPLE action.
>>>
>>> However, instead of sending the sample to an external IPFIX collector
>>> though the network, the sample is emitted using the new action and
>>> made available to locally running sample collector.
>>>
>>> The specific way emit_sample sends the sample (and the way the local
>>> collector shall collect it) is datapath-specific.
>>> Currently, currently only the Linux kernel datapath implements it using
>>> the psample netlink multicast group.
>>>
>>> ~~ Configuration ~~
>>> Local sampling is configured via a new column in the
>>> Flow_Sample_Collector_Set (FSCS) table called "local_sample_group".
>>> Configuring this value is orthogonal to also associating the FSCS
>>> entry to an entry in the IPFIX table.
>>>
>>> Once that entry in the OVSDB is configured, NXAST_SAMPLE actions coming
>>> from the controller will be translated into the following odp action:
>>>
>>> sample(sample={P}%, actions(emit_sample(group={G},cookie={C})))
>>>
>>> Where:
>>> P: Is the sampling probability from NXAST_SAMPLE
>>> G: Is the group id in the FSCS entry whose "id" matches the one in
>>> the NXAST_SAMPLE.
>>> C: Is a 64bit cookie result of concatenating the obs_domain and
>>> obs_point from the NXAST_SAMPLE, i.e:
>>> "obs_domain << 32 | obs_point"
>>> Notes:
>>> - The parent sample action might be omitted if the probability is
>>> 100% and there is no IPFIX sampling that requires the use of a
>>> meter.
>>>
>>> ~~ Internal implementation: dpif-lsample ~~
>>> Internally, a new object called "dpif-lsample" is introduced to track
>>> the configured local sampling exporters and track statistics based on
>>> odp flow stats (using xcache).
>>> It exposes the list of configured exporters and their statistics on a
>>> new unixctl command called "lsample/show".
>>>
>>> ~~ Testing ~~
>>> The series includes an test utility program than can be executed by
>>> running "tests/ovstest test-psample". This utility listens
>>> to packets multicasted by the psample module and prints them (also
>>> printing the obs_domain and obs_point ids).
>>>
>>> ~~ HW Offload ~~
>>> tc offload is not being introduced in this series as existing sample
>>> or userspace actions are not currently offloadable. Also some
>>> improvements need to be implemented in tc for it to be feasible.
>>>
>>> [1]
>>> https://patchwork.kernel.org/project/netdevbpf/cover/[email protected]/
>>
>> Hi Adrian,
>>
>> I did not finish reviewing, but I was doing some testing, and I noticed I’m
>> not getting any warning/error when configuring all of this without Datapath
>> support.
>>
>> Are you planning to add some user feedback when trying to enable this
>> without the kernel other than the “Datapath does not support emit_sample”
>> which the user might not understand relates to this feature?
>>
>
> I added the following code in bridge.c when it configures local
> sampling:
>
>
> + ret = ofproto_set_local_sample(br->ofproto, opts_array, n_opts);
> +
> + if (ret == ENOTSUP) {
> + if (n_opts) {
> + VLOG_WARN_RL(&rl,
> + "bridge %s: ignoring local sampling configuration: "
> + "not supported by this datapath",
> + br->name);
> + }
> + } else if (ret) {
> + VLOG_ERR_RL(&rl, "bridge %s: error configuring local sampling: %s",
> + br->name, ovs_strerror(ret));
> + }
>
> I believe it should warn the user the local sampling configuration will
> not be applied.
>
> Is that not working?
You are right, I did not notice these log messages :( Doing too much stuff in
parallel...
//Eelco
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