RE: Regarding User Data in DPDK ACL Library.

[Konstantin Ananyev <konstantin.ananyev@huawei.com>]

> > > On Thu, 17 Nov 2022 19:28:12 +0530
> > > venkatesh bs <venki.bsv@gmail.com> wrote:
> > >
> > > > Hi DPDK Team,
> > > >
> > > > After the ACL match for highest priority DPDK Classification API
> > > > returns User Data Which is as mentioned below in the document.
> > > >
> > > > 53. Packet Classification and Access Control — Data Plane
> > > > Development Kit
> > > > 22.11.0-rc2 documentation (dpdk.org)
> > > >
> > > >
> > > >    - *userdata*: A user-defined value. For each category, a successful
> > > >    match returns the userdata field of the highest priority matched rule.
> > When
> > > >    no rules match, returned value is zero
> > > >
> > > > I Wonder Why User Data Support does not returns 64 bit values,
> >
> > As I remember if first version of ACL code it was something about space
> > savings to improve performance...
> > Now I think it is more just a historical reason.
> > It would be good to change userdata to 64bit, but I presume it will be ABI
> > breakage.
> Agree. We should support 64b and even 128b (since architectures support 128b atomic operations). This reduces required memory
> barriers required if the data size <= the size of atomic operations.

Hmm...  sorry, didn’t get you  here.
I do understand the user intention to save pointer to arbitrary memory location as user-data (64-bit).
But how does the size of atomic mem-ops relate?
Konstantin