Thanks a lot Asaf, for your answer, so fast.
depending on the feature we want, the table you mentioned in the doc may
give different combinations. Mine, DPDK-20.08/OFED 5.1-2, is part of the
list.
Anyway, my question is more about the API design. Please, find my
comments below.
On 3/29/21 8:02 PM, Asaf Penso wrote:
Hello David,
Thanks for reaching out, I'll try to answer as best as I know and I added Matan
who will be able to provide further info during next week.
First, according to our pmd documentation
(http://doc.dpdk.org/guides/nics/mlx5.html#supported-hardware-offloads) we
recommend using DPDK20.11 and OFED5.2, and not the combo you are referring to.
Second, we can always improve our documentation and I appreciate your queries.
Please see my comments inline.
Regards,
Asaf Penso
-----Original Message-----
From: dev <dev-boun...@dpdk.org> On Behalf Of David Bouyeure
Sent: Monday, March 29, 2021 11:35 AM
To: dev@dpdk.org
Subject: [dpdk-dev] rte_flow ageing
Hi,
I've found out the pretty useful experimental brand new flow ageing API
implemented in the mlx5 PMD.
It is useful and I hope you'll fully understand at the end why 😊
I'm trying it (rte_eth_dev_callback_register(RTE_ETH_EVENT_FLOW_AGED),
RTE_FLOW_ACTION_TYPE_AGE) to recover any flow that I previously
offloaded.
The DPDK version is 20.08 and Mellanox(Connect-X6) OFED drivers are 5.1-
2.5.8.0.
See above the suggested versions for this feature
I eventually don't see the usefulness of the callback since it's actually
triggered
indirectly by us(the DPDK application) when calling
rte_flow_get_aged_flows().
The main intention is to offload the aging logic from the application level to
the pmd level.
There is so saving of cpu cycles, and the gain here is with simplicity.
The application doesn't need to have complex logic of comparison between
counters or other HW info that can be retrieve.
Now, the pmd hides all of that and leaves the application only to decide what
to do with the flows that are aged out.
Please note, the pmd does not delete any flow, just provide the list of all the
flows that are aged.
I fully understand that and this is a very very useful feature to us.
If we don't call it, the callback is called only once.
And, calling rte_flow_get_aged_flows() from the callback won't trigger it next
time(MLX5_AGE_TRIGGER is reset after the callback call)
Once you call the function the pmd will not trigger more events. Now it's up to
the application to decide what to do.
Doing it differently, will cause an interrupt storm and the pmd avoids that.If
new flows are aged then the pmd will trigger a new event.
Sorry, I wasn't realizing that the callback isn't called for each flow
but rather for each port, though it's clear in the PMD code. But, the
fact that we can register several RTE_ETH_EVENT_FLOW_AGED event handlers
is surprising.
So, you suggest to use the callback as an indicator to later retrieve
the aged-out flows, that's it?
Wouldn't calling rte_flow_get_aged_flows with NULL param just to get the
number of aged_flows do the same, without the need to un/register a
callback, and DPDK to call it?
Another thing, the explanation here
http://doc.dpdk.org/api/rte__flow_8h.html#a43763e0794d2696b18b6272619aafc2a
*"...to get the aged flows usynchronously from the event callback..."*
seems wrong to me because age_info->flags is set to 0 just after the
callback, thus ML5_AGE_TRIGGER is canceled and no event will be
triggered before we'll call rte_flow_get_aged_flows() outside of the
callback.
Furthermore, I don't see the point of computing ageing flows in
mlx5_fow.c::mlx5_flow_aging_check() if the client callback isn't called.
Can you elaborate? I'm not sure I understand your intention.
Please forgot :-)
So far, I can handle the flow ageing from the same thread as the one which is
handling the flow direction(rte_flow), it even avoid threads synchronization.
But, in the future, I may need to be noticed as soon as possible of a single
flow
ageing, and thus handle this flow logic from the ageing callback.
I may misunderstand the whole ageing API... Thanks a lot for any clarification.
