[PATCH v2 1/2] eal: provide leading and trailing zero bit count abstraction

[Morten Brørup]

> From: Bruce Richardson [mailto:bruce.richardson at intel.com]
> Sent: Friday, 6 January 2023 12.48
> 
> On Thu, Jan 05, 2023 at 04:32:40PM -0800, Stephen Hemminger wrote:
> > On Thu, 5 Jan 2023 09:21:18 -0800
> > Tyler Retzlaff <roretzla at linux.microsoft.com> wrote:
> >
> > > On Thu, Jan 05, 2023 at 10:01:31AM +0100, Thomas Monjalon wrote:
> > > > 05/01/2023 08:09, Morten Brørup:
> > > > > > From: Tyler Retzlaff [mailto:roretzla at linux.microsoft.com]
> > > > > > +/**
> > > > > > + * @warning
> > > > > > + * @b EXPERIMENTAL: this API may change, or be removed,
> without prior
> > > > > > notice
> > > > > > + *
> > > > > > + * Get the count of leading 0-bits in v.
> > > > > > + *
> > > > > > + * @param v
> > > > > > + *   The value.
> > > > > > + * @return
> > > > > > + *   The count of leading zero bits.
> > > > > > + */
> > > > > > +__rte_experimental
> > > > > > +static inline unsigned int
> > > > > > +rte_clzl(unsigned long v)
> > > > >
> > > > > Don't use l (long) and ll (long long) for names (and types),
> use explicit bit lengths, 32 and 64.
> > > > >
> > > > > E.g.: rte_clz32(uint32_t v)
> > > >
> > > > I agree on using numbers.
> > > >
> > >
> > > love the idea, fewer functions too.
> > >
> > > though it is a shame we cannot adopt C11 standard because we could
> just
> > > do away with the bit suffixes entirely.
> >
> > We could but the project needs to support older RHEL releases
> > which have older tool sets. Though probably this is moot point given
> > how much meson seems to change.
> 
> True, though meson tends to be a bit easier to update than GCC on a
> system
> - no "pip3 install --upgrade gcc", sadly :-)
> 
> If we can't go all the way to C11 support, how about at least going to
> C99
> support? As far as I know DPDK has never updated its minimum C-standard
> version, and it might be a good idea to start the process of doing so,
> even
> if it is a baby step.
> 
> /Bruce

The DPDK Getting Started Guide [1] says:

"Required Tools and Libraries:
[...]
a supported C compiler such as gcc (version 4.9+)"

GCC version 4.9 supports C11 [2]:
"GCC 4.9 Changes: "ISO C11 support is now at a similar level of completeness to ISO C99 support [...]"

So why are we not going to support C11?

Probably because of RHEL 7, which only provides GCC 4.8 [3].

RHEL 7 was released for GA on June 10, 2014 [4]. If someone has a server with a nine year old distro still used in production, it is probably because it is running some legacy application, which is difficult to get up and running on a newer distro. Partial conclusion: RHEL 7 is probably still widely used in production.

However, I have a hard time understanding why anyone would build and/or deploy a brand new DPDK application (based on DPDK 23.03) on such a server. Can someone please justify this?

Are we really going to postpone C11 support in DPDK until June 30, 2026, when RHEL 7 ends its Extended Life Cycle Support [4]?

If so, then the GCC version mentioned in the DPDK Getting Started Guide should be corrected accordingly.

[1]: https://doc.dpdk.org/guides/linux_gsg/sys_reqs.html#compilation-of-the-dpdk
[2]: https://gcc.gnu.org/wiki/C11Status
[3]: https://access.redhat.com/solutions/19458
[4]: https://access.redhat.com/support/policy/updates/errata#Life_Cycle_Dates