[dpdk-dev] [PATCH v6 5/7] power: support callbacks for multiple Rx queues

[Ananyev, Konstantin]

> >
> >> Currently, there is a hard limitation on the PMD power management
> >> support that only allows it to support a single queue per lcore. This is
> >> not ideal as most DPDK use cases will poll multiple queues per core.
> >>
> >> The PMD power management mechanism relies on ethdev Rx callbacks, so it
> >> is very difficult to implement such support because callbacks are
> >> effectively stateless and have no visibility into what the other ethdev
> >> devices are doing. This places limitations on what we can do within the
> >> framework of Rx callbacks, but the basics of this implementation are as
> >> follows:
> >>
> >> - Replace per-queue structures with per-lcore ones, so that any device
> >>    polled from the same lcore can share data
> >> - Any queue that is going to be polled from a specific lcore has to be
> >>    added to the list of queues to poll, so that the callback is aware of
> >>    other queues being polled by the same lcore
> >> - Both the empty poll counter and the actual power saving mechanism is
> >>    shared between all queues polled on a particular lcore, and is only
> >>    activated when all queues in the list were polled and were determined
> >>    to have no traffic.
> >> - The limitation on UMWAIT-based polling is not removed because UMWAIT
> >>    is incapable of monitoring more than one address.
> >>
> >> Also, while we're at it, update and improve the docs.
> >>
> >> Signed-off-by: Anatoly Burakov <anatoly.burakov at intel.com>
> >> ---
> >>
> >> Notes:
> >>      v6:
> >>      - Track each individual queue sleep status (Konstantin)
> >>      - Fix segfault (Dave)
> >>
> >>      v5:
> >>      - Remove the "power save queue" API and replace it with mechanism suggested by
> >>        Konstantin
> >>
> >>      v3:
> >>      - Move the list of supported NICs to NIC feature table
> >>
> >>      v2:
> >>      - Use a TAILQ for queues instead of a static array
> >>      - Address feedback from Konstantin
> >>      - Add additional checks for stopped queues
> >>
> 
> <snip>
> 
> > ....
> >> +static inline void
> >> +queue_reset(struct pmd_core_cfg *cfg, struct queue_list_entry *qcfg)
> >> +{
> >> +     const bool is_ready_to_sleep = qcfg->n_empty_polls > EMPTYPOLL_MAX;
> >> +
> >> +     /* reset empty poll counter for this queue */
> >> +     qcfg->n_empty_polls = 0;
> >> +     /* reset the queue sleep counter as well */
> >> +     qcfg->n_sleeps = 0;
> >> +     /* remove the queue from list of cores ready to sleep */
> >> +     if (is_ready_to_sleep)
> >> +             cfg->n_queues_ready_to_sleep--;
> >> +     /*
> >> +      * no need change the lcore sleep target counter because this lcore will
> >> +      * reach the n_sleeps anyway, and the other cores are already counted so
> >> +      * there's no need to do anything else.
> >> +      */
> >> +}
> >> +
> >> +static inline bool
> >> +queue_can_sleep(struct pmd_core_cfg *cfg, struct queue_list_entry *qcfg)
> >> +{
> >> +     /* this function is called - that means we have an empty poll */
> >> +     qcfg->n_empty_polls++;
> >> +
> >> +     /* if we haven't reached threshold for empty polls, we can't sleep */
> >> +     if (qcfg->n_empty_polls <= EMPTYPOLL_MAX)
> >> +             return false;
> >> +
> >> +     /*
> >> +      * we've reached a point where we are able to sleep, but we still need
> >> +      * to check if this queue has already been marked for sleeping.
> >> +      */
> >> +     if (qcfg->n_sleeps == cfg->sleep_target)
> >> +             return true;
> >> +
> >> +     /* mark this queue as ready for sleep */
> >> +     qcfg->n_sleeps = cfg->sleep_target;
> >> +     cfg->n_queues_ready_to_sleep++;
> >
> > So, assuming there is no incoming traffic, should it be:
> > 1) poll_all_queues(times=EMPTYPOLL_MAX); sleep; poll_all_queues(times=1); sleep; poll_all_queues(times=1); sleep; ...
> > OR
> > 2) poll_all_queues(times=EMPTYPOLL_MAX); sleep; poll_all_queues(times= EMPTYPOLL_MAX); sleep; poll_all_queues(times=
> EMPTYPOLL_MAX); sleep; ...
> > ?
> >
> > My initial thought was 2) but might be the intention is 1)?
> 
> 
> The intent is 1), not 2). There's no need to wait for more empty polls
> once we pass the threshold - we keep sleeping until there's traffic.
> 

Ok, then:
Acked-by: Konstantin Ananyev <konstantin.ananyev at intel.com>

Probably worth to put extra explanation here on in the doc,
to help people avoid wrong assumptions😉