Re: [dpdk-dev] [PATCH v2 1/3] eal/arm64: relax the io barrier for aarch64

[Jerin Jacob <jerinjacobk@gmail.com>]

On Mon, Dec 23, 2019 at 2:44 PM Gavin Hu <Gavin.Hu@arm.com> wrote:
>
> Hi Jerin,

Hi Gavin,

>
> I think we are on the same page with regard to the problem, and the situations, thanks for illuminating the historical background of the two barriers.
> About the solution, I added inline comments.
> > It will be optimization only when if we are changing in the fast path.
> > In the slow path, it does not matter.
> > I think, the First step should be to use rte_cio_* wherever it is
> > coherent memory used in _fast path_. I think, Almost every driver
> > fixed that.
> >
> > I am not against this patch(changing the slow path to use rte_cio*
> > from rte_io* and virtio changes associated with that).
> > If you are taking that patch, pay attention to all the drivers in the
> > tree which is using rte_io* for mixed access in slowpath.
> I see 30+ drivers has calling rte_io* directly or indirectly through rte_write/read*.
> It is hard for me to figure out all the mixed accesses in these drivers, and as you said, it makes no sense to change the _slow path_.
>
> How about we keep the old rte_io as is, and introduce 'fast path' version of rte_io for new code use?
> Then in future, we may merge the two?
> Another reason about this proposal is maybe there is rte_io calling in the fast path, but they are not mixed accesses and rte_cio is not suitable.

Could you share more details about the case where fastpath + rte_io
needed + rte_cio is not suitable?

>
> Any thoughts?
>
> >
> > > But as the case in i40e, we must pay attention to where rte_cio was
> > missing but rescued by old rte_io(but not by new rte_io).
> > >
> > >