[PATCH v3] eventdev: ensure 16-byte alignment for events

[Morten Brørup]

> From: Bruce Richardson [mailto:bruce.richardson at intel.com]
> Sent: Friday, 6 October 2023 12.17
ev: ensure 16-byte alignment for events
> 
> On Fri, Oct 06, 2023 at 12:13:54PM +0200, Morten Brørup wrote:
> > > From: Bruce Richardson [mailto:bruce.richardson at intel.com]
> > > Sent: Friday, 6 October 2023 11.45
> > >
> > > The event structure in DPDK is 16-bytes in size, and events are
> > > regularly passed as parameters directly rather than being passed as
> > > pointers. To help compiler optimize correctly, we can explicitly request
> > > 16-byte alignment for events, which means that we should be able
> > > to do aligned vector loads/stores (e.g. with SSE or Neon) when working
> > > with those events.
> > >
> > > Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
> > > Acked-by: Morten Brørup <mb at smartsharesystems.com>
> > > Acked-by: Jerin Jacob <jerinj at marvell.com>
> > >
> > > ---
> >
> > [...]
> >
> > > +_Static_assert(sizeof(struct rte_event) == 16, "Event structure size is
> not 16-bytes in size");
> >
> > Thank you for adding this extra check. We should have more of these.
> >
> > NB: _Static_assert is deprecated in C23 [1], so for forward compatibility,
> you could use static_assert (which is available in <assert.h>) instead. Nice
> to have; feel free to ignore this comment.
> >
> Is the availability in assert.h backward compatible with C11, since the
> link you posted seems to imply that "static_assert" is only from C23
> onwards?

Yes, the link mentions "static_assert" being available for C11 as a convenience macro in assert.h.

I had to read the link very carefully to get this. I guess I'm not the only one. :-)

I don't object to moving it to the .c file. However, I think it's convenient for readability to have the static_assert close to the thing it checks, and/or close to any code that relies on the assumption it checks.