Re: [RFC 1/8] net/ena: fix warnings related to rte_memcpy and gcc-12

["Michał Krawczyk" <mk@semihalf.com>]

śr., 8 cze 2022 o 17:32 Stephen Hemminger <stephen@networkplumber.org>
napisał(a):
>
> On Wed, 8 Jun 2022 14:29:58 +0200
> Michał Krawczyk <mk@semihalf.com> wrote:
>
> > wt., 7 cze 2022 o 19:17 Stephen Hemminger <stephen@networkplumber.org>
> > napisał(a):
> > >
> > > Rte_memcpy is not needed for small objects only used on control
> > > path. Regular memcpy is as fast or faster and there is more
> > > robust since static analysis etc knows what it does.
> > >
> > > In this driver it was redefining all memcpy as rte_memcpy
> > > which is even worse.
> >
> > Hi Stephen,
> >
> > I would like to shed some light on why we're redefining all the memcpy
> > as rte_memcpy. The ENA HAL is unmodifiable, as it's shared across many
> > platforms and we cannot simply adjust it for the DPDK. We can use the
> > ena_plat_dpdk.h to change the ena_com (HAL) definitions, and that's
> > what we're doing with memcpy. It's being used on the data path for the
> > Tx, to copy the bounce buffers. Following the recommendations in [1]
> > plus the results from [2], we wanted to make use of the optimized
> > memcpy on the ENA's data path as well to reduce the CPU time spent in
> > the PMD. I'm worried that removing rte_memcpy from the ena_plat_dpdk.h
> > will result in some performance degradation for the ENA data path.
> > However I understand your concerns for the control path and I'm ok
> > with it.
> >
> > [1] https://doc.dpdk.org/guides/prog_guide/writing_efficient_code.html#memory
> > [2] https://www.intel.com/content/www/us/en/developer/articles/technical/performance-optimization-of-memcpy-in-dpdk.html
> >
> > Thanks,
> > Michal
> >
>
>
> I admit to having little sympathy unfixable for base/ style code.
> You could have just replaced memcpy() in their with an abstraction layer
> like other drivers.
>

We'll probably end up with the solution you're suggesting. For now
let's remove the memcpy redefinition at all to suppress the warnings.

Acked-by: Michal Krawczyk <mk@semiahalf.com>