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

[Bruce Richardson]

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.

> 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.

Regards,
/Bruce