Re: [dpdk-dev] [PATCH] config/x86: add support for AMD platform

[Thomas Monjalon <thomas@monjalon.net>]

I request a techboard decision for this patch.


02/11/2021 20:04, Thomas Monjalon:
> 02/11/2021 19:45, David Marchand:
> > On Tue, Nov 2, 2021 at 3:53 PM Aman Kumar <aman.kumar@vvdntech.in> wrote:
> > >
> > > -Dcpu_instruction_set=znverX meson option can be used
> > > to build dpdk for AMD platforms. Supported options are
> > > znver1, znver2 and znver3.
> > >
> > > Signed-off-by: Aman Kumar <aman.kumar@vvdntech.in>
> > > ---
> > >  dpdk_conf.set('RTE_CACHE_LINE_SIZE', 64)
> > >  dpdk_conf.set('RTE_MAX_LCORE', 128)
> > >  dpdk_conf.set('RTE_MAX_NUMA_NODES', 32)
> > > +
> > > +# AMD platform support
> > > +if get_option('cpu_instruction_set') == 'znver1'
> > > +    dpdk_conf.set('RTE_MAX_LCORE', 256)
> > > +elif get_option('cpu_instruction_set') == 'znver2'
> > > +    dpdk_conf.set('RTE_MAX_LCORE', 512)
> > > +elif get_option('cpu_instruction_set') == 'znver3'
> > > +    dpdk_conf.set('RTE_MAX_LCORE', 512)
> > > +endif
> > 
> > I already replied to a similar patch earlier in this release.
> > https://inbox.dpdk.org/dev/CAJFAV8z-5amvEnr3mazkTqH-7SZX_C6EqCua6UdMXXHgrcmT6g@mail.gmail.com/
> > 
> > So repeating the same: do you actually _need_ more than 128 lcores in
> > a single DPDK application?

We did not receive an answer to this question.

> Yes I forgot this previous discussion concluding that we should not increase
> more than 128 threads.

We had a discussion yesterday in techboard meeting.
The consensus is that we didn't hear for real need of more than 128 threads,
except for configuration usability convenience.

Now looking again at the code, this is how it is defined:

option('max_lcores', type: 'string', value: 'default', description:
       'Set maximum number of cores/threads supported by EAL;
       "default" is different per-arch, "detect" detects the number of cores on the build machine.')
config/x86/meson.build: dpdk_conf.set('RTE_MAX_LCORE', 128)
config/ppc/meson.build: dpdk_conf.set('RTE_MAX_LCORE', 128)
config/arm/meson.build: it goes from 4 to 1280!

So I feel it is not fair to reject this AMD patch if we allow Arm to go beyond.
Techboard, let's have a quick decision please for 21.11-rc4.


> The --lcores syntax and David's work on rte_thread_register should unblock
> most of use cases.