Re: [dpdk-dev] [PATCH v1 1/6] build: increase default of max lcores to 512

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Sep 10, 2021 at 08:51:04AM +0200, David Marchand wrote:
> On Thu, Sep 9, 2021 at 4:38 PM Bruce Richardson
> <bruce.richardson@intel.com> wrote:
> >
> > On Thu, Sep 09, 2021 at 02:45:06PM +0100, David Hunt wrote:
> > > Modern processors are coming with an ever increasing number of cores,
> > > and 128 does not seem like a sensible max limit any more, especially
> > > when you consider multi-socket systems with Hyper-Threading enabled.
> > >
> > > This patch increases max_lcores default from 128 to 512.
> > >
> > > Signed-off-by: David Hunt <david.hunt@intel.com>
> 
> Why should we need this?
> 
> --lcores makes it possible to pin 128 lcores to any physical core on
> your system.
> And for applications that have their own thread management, they can
> pin thread, then use rte_thread_register.
> 
> Do you have applications that require more than 128 lcores?
>
The trouble is that using the --lcores syntax for mapping high core numbers
to low lcore ids is much more awkward to use. Every case of DPDK use I've
seen uses -c with a coremask, or -l with just giving a few core numbers on
it. This simple scheme won't work with core numbers greater than 128, and
there are already systems available with more than that number of cores.

Apart from the memory footprint issues - which this patch is already making
a good start in addressing, why would we not increase the default
max_lcores to that seen on real systems?

/Bruce