Re: [dpdk-dev] [PATCH 0/4] Extend --lcores to run on cores > RTE_MAX_LCORE

[David Marchand <david.marchand@redhat.com>]

On Mon, Jan 20, 2020 at 7:37 PM Yigit, Ferruh
<ferruh.yigit@linux.intel.com> wrote:
>
> On 12/2/2019 3:35 PM, David Marchand wrote:
> > We are currently stuck with no option but recompile a DPDK if the system
> > has more cores than RTE_MAX_LCORE.
> > A bit of a pity when you get a system with more than 200+ cores and your
> > testpmd has been built and packaged with RTE_MAX_LCORE == 128.
>
> Just for clarification, in this case the DPDK application will work but will
> only use RTE_MAX_LCORE cores, right? You need to compile to use all available cores.

EAL starts up to RTE_MAX_LCORE lcores (as in EAL threads), that's true
before and after this patch.

By default (using the -c or -l options), a lcore X runs on the physical core X.
With the --lcores option, you can select on which physical cores a lcore runs.

But, before this series, the code limits the physical cores to the
same [0, RTE_MAX_LCORE[ range.

>
> Are cores more than RTE_MAX_LCORE usable after this patch?

Yes, see below.


>
> >
> > The --lcores does not need to care about the underlying cores, remove
> > this limitation.
> >
>
> +1 to remove limit in --lcores, but I didn't make it work with this patchset, I
> may be missing something, I tried by setting the "RTE_MAX_LCORE=32", in this
> case should '--lcores "(30-40)@(10-20)"' work?

Quoting the parser code:
 * The format pattern: --lcores='<lcores[@cpus]>[<,lcores[@cpus]>...]'
 * lcores, cpus could be a single digit/range or a group.
 * '(' and ')' are necessary if it's a group.
 * If not supply '@cpus', the value of cpus uses the same as lcores.
 * e.g. '1,2@(5-7),(3-5)@(0,2),(0,6),7-8' means start 9 EAL thread as below
 *   lcore 0 runs on cpuset 0x41 (cpu 0,6)
 *   lcore 1 runs on cpuset 0x2 (cpu 1)
 *   lcore 2 runs on cpuset 0xe0 (cpu 5,6,7)
 *   lcore 3,4,5 runs on cpuset 0x5 (cpu 0,2)
 *   lcore 6 runs on cpuset 0x41 (cpu 0,6)
 *   lcore 7 runs on cpuset 0x80 (cpu 7)
 *   lcore 8 runs on cpuset 0x100 (cpu 8)

With --lcores "(30-40)@(10-20)", you asked to start lcores 30 to 40 to
run on the cpuset 10 to 20.
So it will be refused, since the max lcore is 32.

If your intention was to start lcore 10 on physical core 30, lcore 11
on core 31 etc... then you can try --lcores 10@30,11@31,12@32...


-- 
David Marchand