Re: [dpdk-dev] [dpdk-techboard] [v4 1/3] cryptodev: support enqueue callback functions

[Akhil Goyal <akhil.goyal@nxp.com>]

> 
> Hi Akhil,
> 
> Any updates on this?
> 
There has been no objections for this patch from techboard.

@Thomas Monjalon: could you please review the release notes.
I believe there should be a bullet for API changes to add 2 new fields in rte_cryptodev.
What do you suggest?

@Gujjar, Abhinandan S
Please send a new version for comments on errno.
If possible add cases for deq_cbs as well. If not, send it by next week.

Regards,
Akhil
> > + Ray for ABI
> >
> > <snip>
> >
> > >
> > > On Wed, Oct 28, 2020 at 02:28:43PM +0000, Akhil Goyal wrote:
> > > >
> > > > Hi Konstantin,
> > > >
> > > > > > > Hi Tech board members,
> > > > > > >
> > > > > > > I have a doubt about the ABI breakage in below addition of field.
> > > > > > > Could you please comment.
> > > > > > >
> > > > > > > >  /** The data structure associated with each crypto device.
> > > > > > > > */ struct rte_cryptodev {
> > > > > > > >  	dequeue_pkt_burst_t dequeue_burst; @@ -867,6 +922,10
> > > @@
> > > > > > > > struct rte_cryptodev {
> > > > > > > >  	__extension__
> > > > > > > >  	uint8_t attached : 1;
> > > > > > > >  	/**< Flag indicating the device is attached */
> > > > > > > > +
> > > > > > > > +	struct rte_cryptodev_enq_cb_rcu *enq_cbs;
> > > > > > > > +	/**< User application callback for pre enqueue processing
> > > > > > > > +*/
> > > > > > > > +
> > > > > > > >  } __rte_cache_aligned;
> > > > > > >
> > > > > > > Here rte_cryptodevs is defined in stable API list in map file
> > > > > > > which is a pointer To all rte_cryptodev and the above change
> > > > > > > is changing the size of the
> > > > > structure.
> > > > >
> > > > > While this patch adds new fields into rte_cryptodev structure, it
> > > > > doesn't change the size of it.
> > > > > struct rte_cryptodev is cache line aligned, so it's current size:
> > > > > 128B for 64-bit systems, and 64B(/128B) for 32-bit systems.
> > > > > So for 64-bit we have 47B implicitly reserved, and for 32-bit we
> > > > > have 19B reserved.
> > > > > That's enough to add two pointers without changing size of this struct.
> > > > >
> > > >
> > > > The structure is cache aligned, and if the cache line size in 32Byte
> > > > and the compilation is done on 64bit machine, then we will be left
> > > > with 15Bytes which is not sufficient for 2 pointers.
> > > > Do we have such systems? Am I missing something?
> > > >
> > >
> > > I don't think we support any such systems, so unless someone can point
> > > out a specific case where we need to support 32-byte CLs, I'd tend
> > > towards ignoring this as a non-issue.
> > Agree. I have not come across 32B cache line.
> >
> > >
> > > > The reason I brought this into techboard is to have a consensus on
> > > > such change As rte_cryptodev is a very popular and stable structure.
> > > > Any changes to it may Have impacts which one person cannot judge all
> > > > use
> > > cases.
> > > >
> > >
> > > Haven't been tracking this discussion much, but from what I read here,
> > > this doesn't look like an ABI break and should be ok.
> > If we are filling the holes in the cache line with new fields, it should not be an
> > ABI break.
> >
> > >
> > > Regards,
> > > /Bruce