[PATCH 1/5] config/riscv: add flag for using Zbc extension

[Stanisław Kardach]

On Mon, Oct 7, 2024 at 5:20 PM Stephen Hemminger
<stephen at networkplumber.org> wrote:
>
> On Mon, 7 Oct 2024 10:14:22 +0200
> Stanisław Kardach <stanislaw.kardach at gmail.com> wrote:
>
> > > > >
> > > > > Please do not add more config options via compile flags.
> > > > > It makes it impossible for distros to ship one version.
> > That is a problem with RISC-V in general. Since all features are
> > "extensions" and there is no limit (up to a point) on the permutation
> > of those, we cannot statically build the code for all extensions.
> > Fortunately instructions tend to resolve to nops if an instruction is
> > not present but that still increases the code size for no benefit on
> > platforms without a given extension.
>
> X86 already has the cpu feature flag infrastructure, why not use similar
> mechanism on RiscV?
We can and some further patches I've seen on the list implemented
that. However if that has to be applied in basic intrinsics like
rte_prefetch() which means we'd have to pay a conditional or an
indirect call. It'd be best to test it on a real dataplane platform to
which I don't have access.