On 5/14/24 09:39, Adrian Moreno wrote:
>
>
> On 5/10/24 12:45 PM, Adrian Moreno wrote:
>>
>>
>> On 5/10/24 12:06 PM, Eelco Chaudron wrote:
>>> On 24 Apr 2024, at 21:53, Adrian Moreno wrote:
>>>
>>>> The new odp sample attributes allow userspace to specify a group_id and
>>>> user-defined cookie to be passed down to psample.
>>>>
>>>> Add support for parsing and formatting such action.
>>>>
>>>> Signed-off-by: Adrian Moreno <amore...@redhat.com>
>>>
>>> Hi Adrian,
>>>
>>> See my comments below inline.
>>>
>>> //Eelco
>>>
>>>> ---
>>>> include/linux/openvswitch.h | 49 +++++++++---
>>>> lib/odp-execute.c | 3 +
>>>> lib/odp-util.c | 150 ++++++++++++++++++++++++++---------
>>>> ofproto/ofproto-dpif-ipfix.c | 2 +
>>>> python/ovs/flow/odp.py | 2 +
>>>> tests/odp.at | 5 ++
>>>> 6 files changed, 163 insertions(+), 48 deletions(-)
>>>>
>>>> diff --git a/include/linux/openvswitch.h b/include/linux/openvswitch.h
>>>> index d9fb991ef..3e748405c 100644
>>>> --- a/include/linux/openvswitch.h
>>>> +++ b/include/linux/openvswitch.h
>>>> @@ -696,6 +696,7 @@ enum ovs_flow_attr {
>>>> #define OVS_UFID_F_OMIT_MASK (1 << 1)
>>>> #define OVS_UFID_F_OMIT_ACTIONS (1 << 2)
>>>>
>>>> +#define OVS_PSAMPLE_COOKIE_MAX_SIZE 16
>>>> /**
>>>> * enum ovs_sample_attr - Attributes for %OVS_ACTION_ATTR_SAMPLE action.
>>>> * @OVS_SAMPLE_ATTR_PROBABILITY: 32-bit fraction of packets to sample
>>>> with
>>>> @@ -703,15 +704,27 @@ enum ovs_flow_attr {
>>>> * %UINT32_MAX samples all packets and intermediate values sample
>>>> intermediate
>>>> * fractions of packets.
>>>> * @OVS_SAMPLE_ATTR_ACTIONS: Set of actions to execute in sampling event.
>>>> - * Actions are passed as nested attributes.
>>>> + * Actions are passed as nested attributes. Optional if
>>>> + * OVS_SAMPLE_ATTR_PSAMPLE_GROUP is set.
>>>> + * @OVS_SAMPLE_ATTR_PSAMPLE_GROUP: A 32-bit number to be used as psample
>>>> group.
>>>> + * Optional if OVS_SAMPLE_ATTR_ACTIONS is set.
>>>> + * @OVS_SAMPLE_ATTR_PSAMPLE_COOKIE: A variable-length binary cookie that,
>>>> if
>>>> + * provided, will be copied to the psample cookie.
>>>
>>> Should we mention any limit on the actual length of the cookie?
>>>
>>> Any reason we explicitly call this psample? From an OVS perspective, this
>>> could just be
>>> SAMPLE_ATTR_FORWARD/OFFLOAD/DESTINATION/ENDPOINT/COLLECTOR/TARGET_COOKIE
>>> and
>>> _GROUP. Other datapaths, do not have PSAMPLE.
>>>
>>
>> See my response to your comment on the cover-letter for possible name
>> alternatives.
>>
>>
>>> Thinking about it more, from an OVS perspective we should probably not even
>>> send down a COOKIE, but we should send down an obs_domain_id and
>>> obs_point_id,
>>> and then the kernel can move this into a cookie.
>>>
>>
>> I did consider this. However, the opaque cookie fits well with the tc API
>> which
>> does not have two 32-bit values but an opaque 128-bit cookie. So if the
>> action
>> is offloaded OVS needs to "encode" the two 32-bit values into the cookie
>> anyways.
>>
>>> The collector itself could be called system/local collector, or something
>>> like
>>> that. This way it can use for example psample for kernel and UDST probes
>>> for
>>> usespace. Both can pass the group and cookie (obs_domain_id and
>>> obs_point_id).
>>>
>>> Also, the presence of any of this should not dictate the psample action, we
>>> probably need a specific OVS_SAMPLE_ATTR_SYSTEM_TARGET type nl flag.
>>>
>>
>> It clearer and it might simplify option verification a bit, but isn't a bit
>> redundant? There is no flag for action execution for instance, the presence
>> of
>> the attribute is enough.
>>
>> An alternative would be to have nested attributes, e.g:
>>
>> enum ovs_sample_attr {
>> OVS_SAMPLE_ATTR_UNSPEC,
>> OVS_SAMPLE_ATTR_PROBABILITY, /* u32 number */
>> OVS_SAMPLE_ATTR_ACTIONS, /* Nested OVS_ACTION_ATTR_* attributes. */
>> OVS_SAMPLE_ATTR_SYSTEM, /* Nested OVS_SAMPLE_SYSTEM_ATTR_*
>> attributes. */
>>
>> __OVS_SAMPLE_ATTR_MAX,
>> };
>>
>> enum ovs_sample_system_attr {
>> OVS_SAMPLE_SYSTEM_ATTR_OBS_DOMAIN, /* u32 number */
>> OVS_SAMPLE_SYSTEM_ATTR_OBS_POINT, /* u32 number */
>> OVS_SAMPLE_SYSTEM_ATTR_COOKIE, /* Nested OVS_ACTION_ATTR_*
>>
>> __OVS_SSAMPLE_SYSTEM_ATTR_MAX,
>> };
>>
>> WDYT?
>>
>
> Another benefit of nested attributes is the easier addition of other
> sample-related attributes, I already have a candidate: OVS_SAMPLE_SYSTEM_TRUNC
>
> This will be passed to psample (md->trunc_size) who will truncate the packet
> size to the specified value. This can be useful for large packets for which
> we
> are only interested in the headers.
>
> WDYT?
>
> [snip]
>
Hrm. This makes me think these should not be attributes of a sample action at
all,
but rather we should have a separate EMIT_SAMPLE action that just calls
psample, so
we can combine it with other actions:
sample(..., actions(userspace(...),trunc(100),emit_sample(cookie=...)))
or even:
sample(..., actions(clone(trunc(100),emit_sample(cookie=...)),userspace(...)))
This will also simplify the requires_datapath_assistance() check as we can just
check the action and not iterate over the list of attributes. And it will be
capable to only send this one action to the datapath and not the whole thing.
Naming is still hard though. I like the word "emit" because it doesn't have a
concept of directionality, i.e. we're not sending it to somewhere, we're just
emitting it to the wild. That kind of matches with our vague definition of a
"local" or "system" sampling.
Another option might be 'OUTPUT_SAMPLE/SAMPLE_OUTPUT', i.e. output(sample,
cookie=...).
The main concern is that we already have truncation implemented, so we can be
more
flexible in a way we generate actions instead of adding new attributes.
Thoughts?
Best regards, Ilya Maximets.
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