[PATCH v7] ethdev: add special flags when creating async transfer table

[Ivan Malov]

Hi Thomas,

On Wed, 1 Feb 2023, Thomas Monjalon wrote:

> 31/01/2023 06:30, Ivan Malov:
>> Hi Rongwei,
>>
>> OK, I hear ya. Thanks for persevering.
>>
>> I still hope community will comment on the possibility to
>> provide a hint mechanism for always-the-same match items,
>> with the perspective of becoming more versatile.
>
> Any hint could be imagined.
> But please keep this in mind: a hint is *not* a matching criteria,
> for the simple reason that a hint can be ignored by the PMD.
> So you cannot use a hint to avoid specifying a match item,
> but you could use a hint to specify that an item is the same
> for all the rules of a table.

Reading the same thought expressed in your words, the penny drops.
So, a hint then. But even not being a match criterion itself, it
is still confined to knowledge about a too special particularity.
If one needs to add similar hints for other aspects of matching,
they will have to add more and more bits to this namespace.
So why at all detach the namespace of hints from such of
the match items? A more generic solution might be needed.

In another email of yours, [1], you suggest that documentation be
improved. But it seems that addressing the "fixed match" issue
described by Ori (in the quote) could be that "more generic"
approach. For example, if one added "always_fixed_spec" bit
to struct rte_flow_item, this bit could be taken into
account by PMD in rte_flow_pattern_template_create().
When it has spotted this bit for item ANY_VPORT,
it will treat it the way this "specialise" hint
does, collecting the same upfront knowledge.

Yes, I do acknowledge that encountering such a bit in
a regular/sync flow parsing is irrelevant, but this
is just a general idea and not the final proposal.

Also, in mail [2], Ori talks about separate pipelines
for ingress and egress. That sheds some light on this
hint, thanks. On the one hand, yes, vendors do tend
to have separate pipelines for this, this and this,
but, on the other hand, assuming this particular
separation of pipelines and making a customised
hint for it might not be quite generic. It is
that special particularity which I am talking
about in the first paragraph of my response.

So why not combine addressing "fixed match" items
and solving the problem of this "direction" hint?

Again, I can't come up with an immediate example
of how precisely this could be useful, but since
DPDK strives to being as much generic/neutral as
possible, then why not consider this?

[1] https://mails.dpdk.org/archives/dev/2023-February/260667.html
[2] https://mails.dpdk.org/archives/dev/2023-February/260668.html

>
>
>> Other
>> than that, your current patch might be OK, but, again,
>> I think other reviewers' comments (if any) shall
>> be addressed. But no strong objections from me.
>>
>> By the way, for this "specialise" field, in your opinion,
>> which extra flags could emerge in future / would be nice
>> to have? I mean, is there any concept of what can be
>> added to this field's namespace and what can't be?
>
> I think there is no limit with hint flags to be added.
> I repeat it again: hints can be ignored by the PMDs.
>
>
>

Thank you.