Re: [dpdk-dev] [PATCH v2 2/2] eal: restrict ctrl threads to startup cpu affinity

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

On Tue, Feb 19, 2019 at 12:38 PM Burakov, Anatoly <anatoly.burakov@intel.com>
wrote:

> On 14-Feb-19 1:30 PM, David Marchand wrote:
> > --- a/doc/guides/prog_guide/env_abstraction_layer.rst
> > +++ b/doc/guides/prog_guide/env_abstraction_layer.rst
> > @@ -498,6 +498,20 @@ Those TLS include *_cpuset* and *_socket_id*:
> >   *   *_socket_id* stores the NUMA node of the CPU set. If the CPUs in
> CPU set belong to different NUMA node, the *_socket_id* will be set to
> SOCKET_ID_ANY.
> >
> >
> > +Control Thread API
> > +~~~~~~~~~~~~~~~~~~
> > +
> > +It is possible to create Control Threads using the public API
> ``rte_ctrl_thread_create()``.
> > +Those threads can be used for management/infrastructure tasks and are
> used internally by DPDK for multi process support and interrupt handling.
> > +
> > +Those threads will be scheduled on cpus part of the original process
> cpu affinity from which the dataplane and service lcores are excluded.
> > +
> > +For example, on a 8 cpus system, starting a dpdk application with -l
> 2,3 (dataplane cores), then depending on the affinity configuration which
> can be controlled with tools like taskset (Linux) or cpuset (FreeBSD),
> > +
> > +- with no affinity configuration, the Control Threads will end up on
> 0-1,4-7 cpus.
> > +- with affinity restricted to 2-4, the Control Threads will end up on
> cpu 4.
> > +- with affinity restricted to 2-3, the Control Threads will end up on
> cpu 2 (master lcore, which is the default when no cpu is available).
>
> You're not winning anything by foregoing the 80 char limit on
> documentation (doxygen will still generate this correctly), but you're
> losing in readability when working in terminal. I would prefer if you
> didn't do those long lines :)
>

I don't really care, I will just wait for Thomas opinion.


> Thomas, do we want checkpatch to warn about this?
>
> > +
> >   .. _known_issue_label:
> >
> >   Known Issues
> > diff --git a/lib/librte_eal/common/eal_common_options.c
> b/lib/librte_eal/common/eal_common_options.c
> > index 1f45f82..fca3f83 100644
> > --- a/lib/librte_eal/common/eal_common_options.c
> > +++ b/lib/librte_eal/common/eal_common_options.c
> > @@ -217,6 +217,7 @@ struct device_option {
> >       internal_cfg->create_uio_dev = 0;
> >       internal_cfg->iova_mode = RTE_IOVA_DC;
> >       internal_cfg->user_mbuf_pool_ops_name = NULL;
> > +     CPU_ZERO(&internal_cfg->ctrl_cpuset);
> >       internal_cfg->init_complete = 0;
> >   }
> >
> > @@ -1359,6 +1360,31 @@ static int xdigit2val(unsigned char c)
> >       cfg->lcore_count -= removed;
> >   }
> >
> > +static void
> > +compute_ctrl_threads_cpuset(struct internal_config *internal_cfg)
> > +{
> > +     rte_cpuset_t *cpuset = &internal_cfg->ctrl_cpuset;
> > +     rte_cpuset_t default_set;
> > +     unsigned int lcore_id;
> > +
> > +     for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++) {
> > +             if (eal_cpu_detected(lcore_id) &&
> > +                             rte_lcore_has_role(lcore_id, ROLE_OFF)) {
> > +                     CPU_SET(lcore_id, cpuset);
> > +             }
> > +     }
> > +
> > +     if (pthread_getaffinity_np(pthread_self(), sizeof(rte_cpuset_t),
> > +                             &default_set) < 0)
>
> Shouldn't this be != 0? Manpage doesn't say the error values will be
> negative.
>

Good catch...
/me hides


Thanks for the review.

-- 
David Marchand